High contrast optical film and devices including the same

ABSTRACT

Optical films are disclosed that include a plurality of interference layers. Each interference layer reflects or transmits light primarily by optical interference. The total number of the interference layers is less than about 1000. For a substantially normally incident light in a predetermined wavelength range, the plurality of interference layers has an average optical transmittance greater than about 85% for a first polarization state, an average optical reflectance greater than about 80% for an orthogonal second polarization state, and an average optical transmittance less than about 0.2% for the second polarization state.

TECHNICAL FIELD

The present disclosure relates to a reflective polarizer film, which maybe used in a liquid crystal display.

BACKGROUND

Optical displays are widely used for lap-top computers, hand-heldcalculators, digital watches and the like. The familiar liquid crystaldisplay (LCD) is a common example of such an optical display. In the LCDdisplay, portions of the liquid crystal have their optical state alteredby the application of an electric field. This process generates thecontrast necessary to display “pixels” of information. In some examples,the LCD displays may include combinations of various optical films,including reflective polarizers, to modify the light properties of thedisplay assembly.

LCD displays can be classified based on the type of illumination.“Reflective” displays are illuminated by ambient light that enters thedisplay from the “front.” Typically a brushed aluminum reflector isplaced “behind” the LCD assembly. Another common example is toincorporates a “backlight” assembly for the reflective brushed aluminumsurface in applications where the intensity of the ambient light isinsufficient for viewing. The typical backlight assembly includes anoptical cavity and a lamp or other structure that generates light.Displays intended to be viewed under both ambient light and backlitconditions are called “transflective.” One problem with transflectivedisplays is that the typical backlight is not as efficient a reflectoras the traditional brushed aluminum surface. Further, backlights tend torandomize the polarization of the light and further reduce the amount oflight available to illuminate the LCD display. Consequently, theaddition of the backlight to the LCD display generally makes the displayless bright when viewed under ambient light.

SUMMARY

In some examples, the disclosure describes an optical film that includesa plurality of interference layers, each interference layer reflectingor transmitting light primarily by optical interference, a total numberof the interference layers less than about 1000, such that for asubstantially normally incident light in a predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for a first polarization state, anaverage optical reflectance greater than about 80% for an orthogonalsecond polarization state, and an average optical transmittance lessthan about 0.2% for the second polarization state.

In some examples, the disclosure describes an optical film that includesa plurality of interference layers, each interference layer reflectingor transmitting light primarily by optical interference, a total numberof the interference layers less than about 1000, such that for asubstantially normally incident light in a predetermined wavelengthrange, the optical film has an average optical transmittance (T_(a)) andan average optical reflectance (R_(a)) for a first polarization state(a), and an average optical transmittance (T_(b)) and an average opticalreflectance (R_(b)) for an orthogonal second polarization state (b), aT_(b)/R_(b) less than about 0.002 and a R_(a)/T_(a) less than about0.17.

In some examples, the disclosure describes an optical film that includes(N) sequentially numbered layers, (N) is an integer greater than 200 andless than 1000, each layer having an average thickness less than about200 nm, a fitted curve being a best-fit regression applied to a layerthickness profile plotting a thickness of each layer as a function oflayer number, wherein an average slope of the fitted curve in a regionextending from the first layer to the (Nth) layer being less than about0.2 nm/layer, such that for a substantially normally incident light in apredetermined wavelength range, the optical film has an average opticaltransmittance greater than about 85% for a first polarization state andan average optical reflectance greater than about 80% for an orthogonalsecond polarization state.

In some examples, the disclosure describes an optical film that includes(N) sequentially numbered layers, (N) is an integer greater than 200,with fewer than 10% of the layers having a thickness greater than about200 nm, a fitted curve being a best-fit regression applied to a layerthickness of the optical film as a function of layer number, an averageslope of the fitted curve in a region extending from the first layer tothe (Nth) layer being less than about 0.2 nm.

In some examples, the disclosure describes an optical film that includesa plurality of layers sequentially numbered from one to (N), wherein (N)is an integer greater than 50 and less than 1000, the optical filmtransmitting at least 80% of light having a first polarization state ina predetermined wavelength range and reflecting at least 80% of lighthaving an orthogonal second polarization state in the predeterminedwavelength range, a fitted curve being a best-fit regression applied toa layer thickness of the optical film as a function of layer number,such that in a region extending from the first layer to the (Nth) layer,a difference between a maximum slope and a minimum slope of the fittedcurve is less than about 0.70 nm/layer where the maximum slope and theminimum slope are each evaluated over any group of 25 to 50 adjacentlayers.

In some examples, the disclosure describes an optical film transmittingat least 80% of light having a first polarization state in apredetermined wavelength range and reflecting at least 80% of lighthaving an orthogonal second polarization state in the predeterminedwavelength range, the optical film includes a stack of (N) layers,wherein (N) is an integer greater than 50 and less than 1000, such that,for a plurality of non-overlapping groups of sequentially arrangedlayers in the stack of (N) layers, the layers in each group numberedfrom one to (m), (m) being greater than 25, for each non-overlappinggroup a fitted curve is a best-fit regression applied to a layerthickness of the group as a function of layer number, wherein in aregion extending from the first layer in the group to the (mth) layer inthe group, the fitted curve has an average slope such that, a maximumdifference between the average slopes of the fitted curves in theplurality of non-overlapping groups is less than 0.70 nm/layer.

In some examples, the disclosure describes an optical film that includesa plurality of alternating first and second layers, each first layer andeach second layer reflecting or transmitting light primarily by opticalinterference, a total number of each of the first and second layersbeing less than 400 and greater than 100, for each pair of adjacentfirst and second layers: in a plane of the first layer, the first layerhas a maximum index of refraction n1_(x) along an x-direction, thesecond layer has an index of refraction n2_(x) along the x-direction, adifference between n1_(x) and n2_(x) is greater than about 0.24, and amaximum angular range of the x-directions of the first layers is lessthan about 2 degrees.

In some examples, the disclosure describes an optical film that includesa plurality of alternating higher index of refraction and lower index ofrefraction interference layers, each interference layer reflecting ortransmitting light primarily by optical interference, a total number ofthe interference layers greater than 300, an optical power of theoptical film per interference layer greater than about 0.7.

In some examples, the disclosure describes an optical film that includesa plurality of alternating higher index of refraction and lower index ofrefraction interference layers, each interference layer reflecting ortransmitting light primarily by optical interference, an optical powerof the plurality of the interference layers per interference layer beinggreater than (−0.0012*N+1.46), where (N) is a total number of thealternating higher index of refraction and lower index of refractioninterference layers, (N) being greater than 100 and less than 1000.

In some examples, the disclosure describes an optical film that includesa plurality of interference layers reflecting and transmitting lightprimarily by optical interference, such that for a substantiallynormally incident light in a predetermined wavelength range, theplurality of the interference layers transmit at least 80% of lighthaving a first polarization state, reflect at least 80% of light havingan orthogonal second polarization state, and have an average opticaldensity greater than about 2.5, the plurality of the interference layersdivided into a plurality of optical stacks, each pair of adjacentoptical stacks separated by one or more spacer layers not reflecting ortransmitting light primarily by optical interference, each optical stacktransmitting at least 50% of light having the first polarization statein the predetermined wavelength range and reflecting at least 50% oflight having the second polarization state in the predeterminedwavelength range, the interference layers in each optical stacksequentially numbered, each optical stack having a best-fit linearequation correlating a thickness of the optical stack to interferencelayer number, the linear equation having an average slope in a regionextending from the first interference layer in the stack to the lastinterference layer in the stack, a maximum difference between theaverage slopes of the linear equations of the plurality of opticalstacks being less than about 20%

In some examples, the disclosure describes an optical film transmittingat least 80% of light having a first polarization state in apredetermined wavelength range and reflecting at least 80% of lighthaving an orthogonal second polarization state in the predeterminedwavelength range, the optical film includes: no less than 200 and nogreater than 400 sequentially arranged unit cells, each unit cellcomprising a lower index or refraction first layer and an adjacenthigher index of refraction second layer, a difference between the higherand lower indices of refraction for each unit cell greater than about0.24, each unit cell having a total optical thickness equal to one halfof a central wavelength in a predetermined wavelength range, such thatfor each of at least 80% of pairs of adjacent unit cells in thesequentially arranged unit cells, a ratio of a difference of the centralwavelengths of adjacent unit cells to an average of the centralwavelengths of the adjacent unit cells is less than about 2%.

In some examples, the disclosure describes an optical film that includesa plurality of interference layers reflecting or transmitting lightprimarily by optical interference in a predetermined wavelength range, amaximum difference between indices of refraction of the interferencelayers being Δn, a fitted curve being a best-fit regression applied to alayer thickness of the optical film as a function of layer number, thefitted curve having an average slope K in a region extending across theplurality of interference layers, Δn/K greater than about 1.2.

In some examples, the disclosure describes an optical film that includes(M_(a)) sequentially arranged first unit cells optimized to transmit orreflect light in a first, but not second, predetermined wavelengthrange, each of the first unit cells comprising a first high index ofrefraction layer and a second low index of refraction layer, and (M_(b))sequentially arranged second unit cells optimized to transmit or reflectlight in the second, but not the first, predetermined wavelength range,each of the second unit cells comprising a third high index ofrefraction layer and a fourth low index of refraction layer, such that:for the (M_(a)) sequentially arranged first unit cells, a ratio of anaverage of indices of refraction of the first high index of refractionlayers to an average of indices of refraction of the second low index ofrefraction layers times (M_(a)) is greater than about 300, and for the(M_(b)) sequentially arranged second unit cells, a ratio of an averageof indices of refraction of the third high index of refraction layers toan average of indices of refraction of the fourth low index ofrefraction layer times (M_(b)) is greater than about 300, where forlight incident on the optical film at any incidence angle from aboutzero degree to about 30 degrees having any wavelength in the first andsecond predetermined wavelength ranges, a ratio of an average opticaltransmittance (T_(a)) of the optical film for a first polarization stateto an average optical transmittance (T_(b)) of the optical film for anorthogonal second polarization state is no less than about 1000:1.

In some examples, the disclosure describes a display assembly thatincludes a light source, a liquid crystal display assembly, and one ofthe preciously described optical films disposed between the liquidcrystal display assembly and the light source.

In some examples, the disclosure describes a display assembly thatincludes a light source, a liquid crystal layer configured to beilluminated by the light source, one or more brightness enhancementfilms disposed between the light source and the liquid crystal layer forincreasing an axial brightness of the display assembly, and a reflectivepolarizer disposed between the one or more brightness enhancement filmsand the liquid crystal layer and configured to substantially transmitlight having a first polarization state and substantially reflect lighthaving an orthogonal second polarization state, the reflective polarizerhaving an average optical transmittance less than about 0.2% for thesecond polarization state, wherein no absorbing polarizer is disposedbetween the light source and the liquid crystal layer, and wherein acontrast ratio of the display assembly is at least twice that of acomparative display assembly having the same construction except thatthe average transmittance of the reflective polarizer of the comparativedisplay assembly for the second polarization state is greater than about1.0%.

In some examples, the disclosure describes a display assembly thatincludes a light source, a liquid crystal layer configured to beilluminated by the light source, one or more brightness enhancementfilms disposed between the light source and the liquid crystal layer forincreasing an axial brightness of the display assembly, and a reflectivepolarizer disposed between the one or more brightness enhancement filmsand the liquid crystal layer and comprising a plurality of interferencelayers transmitting or reflecting light primarily by opticalinterference, such that for a substantially normally incident light in apredetermined wavelength range, the plurality of the interference layerstransmits at least 80% of light having a first polarization state andtransmits less than about 0.2% of light having an orthogonal secondpolarization state, wherein no absorbing polarizer is disposed betweenthe light source and the liquid crystal layer.

In some examples, the disclosure describes an optical stack including areflective polarizer including a plurality of interference layers, eachinterference layer reflecting or transmitting light primarily by opticalinterference, for a substantially normally incident light having apredetermined wavelength, the plurality of interference layers having anoptical transmittance greater than about 85% for a first polarizationstate, an optical reflectance greater than about 80% for an orthogonalsecond polarization state, and an optical transmittance less than about0.1% for the second polarization state; and an absorbing polarizerbonded to and substantially co-extensive with the reflective polarizer,for a substantially normally incident light having the predeterminedwavelength, the absorbing polarizer having a first optical transmittancefor the first polarization state, an optical absorption greater thanabout 50% for the second polarization state, and a second opticaltransmittance for the second polarization state, a ratio of the secondoptical transmittance to the first optical transmittance being greaterthan about 0.001.

In some examples, the disclosure describes an optical system fordisplaying an object to a viewer centered on an optical axis andincluding: at least one optical lens having a non-zero optical power;

a reflective polarizer disposed on and conforming to a first majorsurface of the optical lens, the reflective polarizer substantiallytransmitting light having a first polarization state and substantiallyreflecting light having an orthogonal second polarization state; and apartial reflector disposed on and conforming to a different second majorsurface of the optical lens, the partial reflector having an averageoptical reflectance of at least 30% for a predetermined wavelengthrange, such that an average optical transmittance of the optical systemfor an incident light along the optical axis having the secondpolarization state is less than about 0.1%.

In some examples, the disclosure describes a polarizing beam splitter(PBS) including: a first and second prism; and a reflective polarizerdisposed between and adhered to the first and second prisms, thereflective polarizer substantially reflecting polarized light having afirst polarization state and substantially transmitting polarized lighthaving an orthogonal second polarization state, such that when anincident light having a predetermined wavelength enters the PBS from aninput side of the PBS and exits the PBS from an output side of the PBSafter encountering the reflective polarizer at least once, a ratio of anaverage intensity of the exiting light to an average intensity of theincident light is: greater than about 90% when the incident light hasthe first polarization state, and less than about 0.2% when the incidentlight has the second polarization state.

In some examples, the disclosure describes a liquid crystal displayprojection system including the optical film as described herein.

In some examples, the disclosure describes a display assembly including:a light source; a liquid crystal layer configured to be illuminated bythe light source; and a reflective polarizer including the optical filmof any one of clauses 1 to 126, the reflective polarizer disposedadjacent to the liquid crystal layer.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an example optical film that includes a plurality ofinterference layers sequentially numbered 1 to (N).

FIG. 2 is a schematic perspective diagram of a segment of the opticalfilm of FIG. 1 illustrating the alternating interference layers.

FIG. 3 is a plot of an example thickness profile of the optical film ofFIG. 1.

FIG. 4A shows another example of optical film that can be formed toexhibit one or more of the optical properties described herein.

FIG. 4B is a plot of an example thickness profile of the optical film ofFIG. 4A.

FIG. 4C is a pair of plots of an example thickness profile of theoptical film of FIG. 4A.

FIGS. 5A and 5B are a representative transmission plots for an exampleoptical films in accordance with the disclosure.

FIG. 6 shows another example of optical film that can be formed toexhibit one or more of the optical properties described herein.

FIG. 7 is a diagram of an example display assembly that includes areflective polarizer optical film, a liquid crystal display assembly,and a light source.

FIG. 8 is an example brightness profile for display assembly of FIG. 7.

FIG. 9 is a plot showing the layer profile for Example 1.

FIG. 10 is a schematic cross-sectional view of an example optical systemincluding an optical film in the form of a reflective polarizer.

FIG. 11 is a schematic cross-sectional view of an example polarized beamsplitter including an optical film in the form of a reflectivepolarizer.

FIG. 12 is a plot of example thickness profiles (layer thickness vslayer number) for example reflective polarizer films as described hereincompared to conventional reflective polarizer films.

FIG. 13 is a show a plot of the layer thickness profile for the opticalfilm of Example 7.

FIG. 14 shows a plot of the block state transmission (T_(b)) for thefilm of Example 6 over the wavelength range of 375-850 nm.

FIG. 15 shows the optical power per layer versus the number of layersfor the non-limiting optical films of Examples 1 and 4 prepared inaccordance with the disclosure compared to the comparative examples ofTable 6.

DETAILED DESCRIPTION

The optical films described herein may be used in display assemblies toenhance the brightness of the display when viewed under ambient light,reduce the overall thickness of the display assembly, or provide otheruseful advantages. In some examples, the optical films described hereinmay be used as a reflective polarized that demonstrates a relativelyhigh contrast ratio of incident light within a desired wavelength rangetransmitted through the optical film within a pass polarization statecompared to the light transmitted through the film in an orthogonalreflected polarization state. In some examples, the described opticalfilms may exhibit a contrast ratio of at least 1000:1, while using arelatively small number of total optical layers (e.g., no more than 1000total layers). In some examples, the properties and construction of theoptical films describe herein may provide reflective polarizerexhibiting a high contrast ratio while having an overall thickness thatremains significantly low (e.g., less than about 100 μm).

The optical films described herein may be characterized as a multi-layeroptical film having plurality of optical layers (e.g., interferencelayers) configured to selectively transmit and reflect light within apredetermined wavelength range. In some such examples, the optical filmsmay function as a reflective polarizer or RP that selectively transmitsand reflects light of different polarization states. For example, FIG. 1is a schematic perspective view of an example of a multi-layer opticalfilm 100 that includes a plurality interference layers 102 positionedalong a central axis to form optical film 100 having a total of (N)interference layers 102. The figure includes a coordinate system thatdefines X, Y, and Z directions that are referred to in the perception ofoptical film 100.

During use, light incident on a major surface of optical film 100 (e.g.,film surface 104), depicted by incident light 110 may enter a firstlayer of optical film 100 and propagate through the plurality ofinterference layers 102, undergoing select reflection or transmission byoptical interference depending on the polarization state of incidentlight 110. Incident light 110 may include a first polarization state (a)and a second polarization state (b) that are be mutually orthogonal toone another. The first polarization state (a) may be considered as the“pass” state while the second polarization state (b) may be consideredas the “reflected” state. As incident light 110 propagates throughplurality of interference layers 102, a portion of the light in thesecond polarization state (b) will be reflected by the layers summatingin second polarization state (b) being reflected by optical film 100while a portion of the light in the first polarization state (a)collectively passes through optical film 100.

In some examples, the optical film 100 may be characterized in terms ofits reflectivity and transmissivity of the first and second polarizationstates (a) and (b) of incident light 110. For example, the amount ofincident light 110 for a predetermined wavelength transmitted throughoptical film 100 may be expressed as the percent of opticaltransmittance (T_(a)) for the first polarization state (a) and thepercent of optical transmittance (T_(b)) for the second polarizationstate (b), orthogonal to T_(a). The amount of incident light 110 for apredetermined wavelength range reflected by optical film 100 may beexpressed as the percent of optical reflectance (R_(a)) for the firstpolarization state (a) and the percent of optical reflectance (R_(b))for the second polarization state (b), orthogonal to T_(a). For a givenoptical film, the sum of transmissivity, reflectivity, and losses dueto, for example, absorption, will amount to 100% for light within apredetermined wavelength range. In the present disclosure, optical film100 may have a relatively low absorbance for light within thepredetermined wavelength range. In some examples, the relatively lowabsorbance of incident light 110 by optical film 100 may result lessheat generated within optical film 100 and leading to an overall moreefficient reflective film.

The predetermined wavelength range may be any suitable wavelength range,including for example, visible light (e.g., about 400-700 nm),near-infrared (e.g., about 800-1300 nm), a range based on the output ofa liquid crystal display backlight (425-675 nm), or the like. In someexamples, optical film 100 may be configured to transmit and reflectlight of different polarizations states within more than onepredetermined wavelength range, e.g., visible light and near-infrared.For example, the predetermined wavelength range may include a firstrange from about 430 nm to about 465 nm, a second range from about 490nm to about 555 nm, and a third range from about 600 nm to about 665 nm.In some such examples, optical film 100 may include multiplestack/packets as described further below with respect to FIG. 4, thateach include a plurality of interference layers, where each stack/packetmay be directed to a different predetermined wavelength range.

In some examples, as described further below, the interference layersmay be characterized as a series of two-layer unit cells. The thicknessof each unit cell may be configured to reflect a target wavelengthwithin the predetermined wavelength range. In some examples, the centralwavelength of reflectivity for a unit cell corresponds to the twice theoptical thickness of a two-layer unit cell. Therefore, to reflect apredetermined wavelength range (e.g. 400 to 1000 nm), the unit cellswithin the stacks/packets will have difference thicknesses to cover theleft band-edge, the right band-edge, and wavelengths in-between.

In some non-limiting examples, optical film 100 may include less thanabout 1000 (N) interference layers 102, each interference layer 102reflecting or transmitting incident light 110 primarily by opticalinterference. While an optical film 100 with less than 1000 (N) totalinterference layers 102 is provided as one example, in some example,optical film 100 may include more than 1000 total interference layers102 and still obtain some of the described optical properties. In otherexamples, it may be desirable to achieve the desired optical performanceusing fewer total layers in order to reduce the overall thickness of thefilm as reducing the overall thickness of a display assembly (e.g., LCDdisplays) is preferable in may application. Additionally oralternatively, the fewer total number of interference layers 102 mayreduce the complexity in of the manufacturing process as well as reducethe potential for introducing variability (e.g., spectral variability inblock or pass states) or production errors (e.g., increased block statetransmission due to depolarization between the layers, reduced passstate transmission, or the like) in the final optical film. In someexamples, optical film 100 may include less than 900 (N) total layers,or less than 800 (N) total layers in other layers.

In some such examples, using less than about 1000 total (N) interferencelayers 102, the optical film may have an average optical transmittance(T_(a)) greater than about 85% for a first polarization state (a), anaverage optical reflectance (R_(b)) greater than about 80% for anorthogonal second polarization state (b), and an average opticaltransmittance (T_(b)) less than about 0.2% for the second polarizationstate (b) for a substantially normally incident light 110 in apredetermined wavelength range.

In some examples, optical film 100 may be characterized in terms of theoptical transmittance or reflectance the film. In some examples, theaverage optical transmittance (T_(a)) for the first/pass polarizationstate (a) of optical film 100 for incident light 110 (e.g., from airinto optical film 100) within a predetermined wavelength range may begreater than about 85%, in some examples greater than 87%, and in someexamples, greater than 89% using no more than 1000 total (N)interference layers 102. In some examples, the average opticaltransmittance (T_(b)) for the second/reflected polarization state (b) ofoptical film 100 for incident light 110 within a predeterminedwavelength range may be less than about 0.15%, and in some examples,less than 0.10% using no more than 1000 total (N) interference layers102.

In some examples, optical film 100 may be characterized in terms of theoptical transmittance through the plurality of interference layers 102(e.g., ignoring any loss associated with reflectance at the air-filminterface). In some examples, the average optical transmittance (T_(a))for the first/pass polarization state (a) through plurality ofinterference layers 102 for incident light 110 within a predeterminedwavelength range may be greater than about 90%, in some examples greaterthan 95%, and in some examples, greater than 98% using less than 1000total (N) interference layers 102.

The properties and construction of optical film 100 may provide the filmwith a relatively high contrast ratio. The contrast ratio may be definedas the ratio between the normal axis incident light 110 transmittedthrough optical film 100 in the first polarization state (a) (e.g., the“pass” state) divided by normal axis incident light 110 transmittedthrough optical film 100 in the second orthogonal polarization state (b)(e.g., the “reflected” state) for a specified wavelength range.

In some examples, the degree of transmittance and reflectance of opticalfilm 100 may be characterized in terms of the ratio of thetransmissivity to reflectivity for a given polarization state. Forexample, the ratio of the percent of optical transmittance to thepercent of optical reflectance for the first polarization state (a) maybe expressed as (R_(a)/T_(a)) for incident light 110 within apredetermined wavelength range and the ratio of the percent of opticaltransmittance to the percent of optical reflectance for the for thesecond polarization state (b) for incident light 110 within thepredetermined wavelength range may be expressed as (T_(b)/R_(b)). Insome examples, R_(a)/T_(a) ratio may be relatively low, e.g., less thanabout 0.17, and the T_(b)/R_(b) ratio may be relatively low, e.g., lessthan about 0.002.

In some non-limiting examples, optical film 100 a total (N) of less thanabout 1000 interference layers 102 that reflect or transmit lightprimarily by optical interference such that for a substantially normallyincident light 110 in a predetermined wavelength range, the T_(b)/R_(b)ratio for optical film 100 is less than about 0.002 (e.g., less than0.001) and R_(a)/T_(a) is less than about 0.017 (e.g., less than 0.14),where T_(a) and R_(a) are the average optical transmittance andreflectance respectively for the first polarization state (a) (e.g., the“pass” state), and T_(b) and R_(b) are the average optical transmittanceand reflectance respectively for the second polarization state (b)(e.g., the “block” state) for incident light 110 in the predeterminedwavelength range.

In some examples, optical film 100 may be characterized in terms of theratio between the percent of optical transmittance for the first (a) andsecond (b) polarization states. For example, the ratio T_(a)/T_(b)representing the optical transmittance for the first (a) and second (b)polarization states optical film 100 may be greater than about 425.

Additionally or alternatively optical film 100 may be characterized interms of the ratio between the percent of optical reflectance for thesecond (b) and first (a) polarization states. For example, the ratioR_(b)/R_(a) representing the optical reflectance for the second (b) andfirst (a) polarization states optical film 100 may greater than about6.7.

In some examples, the transmittance and reflectance properties ofoptical film 100 may be characterized for incident light within apredetermined wavelength range having an angle of incidence on surface104 within a set angle of less than about 30°, for example, less thanabout 20°, or less than about 10°, with the incidence angle measuredfrom the normal of surface 104 with 0° representing the normal. Forexample, in some non-limiting examples, light incident on surface 104 ofoptical film 100 at an incidence angle of less than about 10° within apredetermined wavelength range (e.g., visible light of about 400 nm toabout 700 nm) may undergo an average optical transmittance (T_(a)) ofgreater than about 85% for the first polarization state (a), an averageoptical reflectance (R_(b)) of greater than about 80% for the secondpolarization state (b), and an average optical transmittance (T_(b)) ofless than about 0.2% for the second polarization state (b).

In some examples, interference layers 102 of optical film 100 mayinclude alternating layers (e.g., A and B) of two different polymericmaterials that exhibit differing index of refraction characteristics.For example, FIG. 2 is a schematic perspective diagram of a segment ofthe optical film 100 illustrating alternating interference layers 102 aand 102 b. FIG. 2 includes a coordinate system that defines X, Y, and Zaxes to assist with describing the optical properties of optical film100.

As shown in FIG. 2, optical film 100 includes of alternating layers(e.g., ABABA . . . ) of different optical materials referred to asmaterial “(A)” and material “(B)” throughout the drawings anddescription. As described further below, the various layers of the twodifferent materials may be formed through an extrusion/laminationprocess in which the layers are extruded together to form the multipleoptical layers 102 (ABABA . . . ) that are adhered together.

In some examples, during the extrusion process the optical layers 102may be stretched to impart the various interference characteristics ofthe film. For example, layers of the A and B optical material may bestretched (e.g., in a 5:1 ratio or a 6:1 ratio) along one axis (e.g.,the X-axis), and not stretched appreciably (1:1) along the orthogonalaxis (e.g., the Y-axis). The X-axis is referred to as the “stretched”direction while the Y-axis is referred to as the “transverse” direction.

The selection of optical material used to form the A and B layers may beselected to impart specific optical characteristics to the film as aresult of the stretching process. For example, the (B) material formingoptical layers 102 b may have a nominal index of refraction (e.g.,n2=1.64) which is not substantially altered by the stretching process.As such, the index or refraction for “B” layers 102 b in both the x andy directions (n2_(x) and n2_(y)) may be substantially the same for bothdirections after the stretching process. In contrast, the (A) materialforming optical layers 102 a may have an index of refraction altered bythe stretching process. For example, a uniaxially stretched layer 102 aof the (A) material may have a higher index of refraction in the X-axisor stretched direction 120 (e.g., n1_(x)=1.88), and a different index ofrefraction associated with the Y-axis or non-stretched direction 122(e.g., n1_(y)=1.64). Due to the increased index of refraction in thestretched direction, layers 102 a including material (A) may beconsidered as the high index of refraction (HIR) layers 102 a whileinterference layers 102 b including material (B) may be considered asthe low index of refraction (LIR) layers 102 b. In some examples, therefractive indices of the alternating AB layers may be may be controlledby judicious materials selection and processing conditions. In someexamples, the optical characteristics of the layers 102 may causeoptical film 100 to act as a reflecting polarizer that willsubstantially transmit the first polarization state (a) component ofincident light 110 within a predetermined wavelength range oriented withrespect to the non-stretched axis 122, while the stretched axis 120,will correspond to the reflect-axis for which the component of incidentlight 110 in second polarization state (b) within the predeterminedwavelength range will be substantially reflected through opticalinterference.

In some examples, optical film 100 may be characterized by thedifference between the indices of refraction between alternating HIRlayers 102 a and LIR layers 102 b along the stretched axis 120 (i.e.,Δn_(x)=n1_(x)−n2_(x)). In some such examples, the indices of refractionbetween alternating HIR layers 102 a and LIR layers 102 b along thenon-stretched axis direction 122 may be substantially the same such thatthe difference between the indices in non-stretched axis direction 122(i.e., Δn_(y)=n1_(y)−n2_(y)) is about 0.0. In some examples, increasingthe Δn_(x) between HIR and LIR layers 102 a, 102 b may permit sufficienttransmission/reflection of polarized light for a given wavelength rangeusing a fewer total number of interference layers as compared to anoptical film with a lower Δn_(x) for with the same optical power.

Preferably, the stretched axis direction of each of interference layers102 will be substantially aligned (e.g., aligned or nearly aligned) suchthat the X-axis for each respective layer 102 represents the directionfor obtaining the maximum index of refraction within the X-Y plane (FIG.2) for each layer. However due to machine tolerances and number ofinterference layers 102, the stretched axis 120 for each of theinterference layers (e.g., representing the direction of obtaining themaximum index or refraction for the layer) may be aligned to within avariance of about ±2°.

In some non-limiting examples, optical film 100 may include a total ofmore than 200 and less than 1000 (N) first layers 102 a and secondlayers 102 b that reflect or transmit light primarily by opticalinterference. For example, optical film 100 may include less than 400and greater than 100 first layers 102 a and less than 400 and greaterthan 100 second layers 102 b. In some such examples, for each pair ofadjacent first and second layers 102 a, 102 b, the layers may define astretched axis that represents the direction in which the maximum indexof refraction obtained for the respective layer (e.g., X-axis/direction120 corresponding to indices of refraction n1_(x) and n2_(x) for the twolayers). The difference of indices of refraction between the first layer102 a and second layer 102 b for the primary axis (e.g.,Δn_(x)=n1_(x)−n2_(x)) may be greater than about 0.24. In some suchexamples, the respective stretched axis directions for each of first andsecond optical layers 102 a, 102 b may be substantially aligned suchthat interference layers 102 define a maximum angular range of therespective stretched-axis directions of less than about 2 degrees.

Optical film 100 including plurality of interference layers 102 may beformed using any suitable technique. For example, layers 102 a and 102 bincluding optical materials A and B respectively may be fabricated usingcoextruding, casting, and orienting processes to form stacks/packets oftens to hundreds of interference layers 102, followed stretching orotherwise orienting the extruded layers to form a stack/packet ofinterference layers 102. Each stack/packet may include between about 200and 1000 total interference layers depending on the desiredcharacteristics of optical film 100. As used herein a “stack/packet” isused to refer to a continuous set of alternating interference layers 102a, 102 b that is absent of any spacer or non-interference layers formedwithin the stack/packet (e.g., sequentially arranged). In some examples,spacer, non-interference layers, or other layers may be added to theoutside of a given stack/packet, thereby forming the outer layers of thefilm without disrupting the alternating pattern of interference layers102 within the stack/packet.

In some examples, optical film 100 may be fabricated by coextrusion. Thefabrication method may comprise: (a) providing at least a first and asecond stream of resin corresponding to the first and second polymers tobe used in the finished film; (b) dividing the first and the secondstreams into a plurality of layers using a suitable feedblock, such asone that comprises: (i) a gradient plate comprising first and secondflow channels, where the first channel has a cross-sectional area thatchanges from a first position to a second position along the flowchannel, (ii) a feeder tube plate having a first plurality of conduitsin fluid communication with the first flow channel and a secondplurality of conduits in fluid communication with the second flowchannel, each conduit feeding its own respective slot die, each conduithaving a first end and a second end, the first end of the conduits beingin fluid communication with the flow channels, and the second end of theconduits being in fluid communication with the slot die, and (iii)optionally, an axial rod heater located proximal to said conduits; (c)passing the composite stream through an extrusion die to form amultilayer web in which each layer is generally parallel to the majorsurface of adjacent layers; and (d) casting the multilayer web onto achill roll, sometimes referred to as a casting wheel or casting drum, toform a cast multilayer film. This cast film may have the same number oflayers as the finished film, but the layers of the cast film aretypically much thicker than those of the finished film.

After cooling, the multilayer web can be re-heated and drawn orstretched to produce the near-finished multilayer optical film. Thedrawing or stretching accomplishes two goals: it thins the layers totheir desired final thicknesses profile, and it orients the layers suchthat at least some of the layers become birefringent. The orientation orstretching can be accomplished along the cross-web direction (e.g. via atenter), along the down-web direction (e.g. via a length orienter), orany combination thereof, whether simultaneously or sequentially. Ifstretched along only one direction, the stretch can be “unconstrained”(wherein the film is allowed to dimensionally relax in the in-planedirection perpendicular to the stretch direction) or “constrained”(wherein the film is constrained and thus not allowed to dimensionallyrelax in the in-plane direction perpendicular to the stretch direction).If stretched along both in-plane directions, the stretch can besymmetric, i.e., equal along the orthogonal in-plane directions, orasymmetric. Alternatively, the film may be stretched in a batch process.In any case, subsequent or concurrent draw reduction, stress or strainequilibration, heat setting, and other processing operations can also beapplied to the film.

The polymers of the various layers are preferably chosen to have similarrheological properties, e.g., melt viscosities, so that they can beco-extruded without significant flow disturbances. Extrusion conditionsmay be chosen to adequately feed, melt, mix, and pump the respectivepolymers as feed streams or melt streams in a continuous and stablemanner. Temperatures used to form and maintain each of the melt streamsmay be chosen to be within a range that avoids freezing,crystallization, or unduly high pressure drops at the low end of thetemperature range, and that avoids material degradation at the high endof the range.

Example (A) materials suitable for optical film 102 may include, forexample, polyethylene naphthalate (PEN), copolymers containing PEN andpolyesters (e.g., polyethylene terephthalate (PET) or dibenzoic acid),glycol modified polyethylene terephthalate, or the like. Example (B)materials suitable for optical film 102 may include, for example,copolyesters based on PEN, copolyesters based on PET, polycarbonate(PC), or blends of these three classes of materials, or the like. Toachieve high reflectivities with a reasonable number of layers, adjacentmicrolayers can exhibit a difference in refractive index (Δn_(x)) forlight polarized along the x-axis of at least 0.2 in addition to thethickness profile described below.

In some examples, stretched axis 122 (e.g., Y-axis of FIG. 2) for eachrespective HIR and LIR layer 102 a, 102 b of plurality of interferencelayers 102 may be substantially aligned with one another (e.g., alignedin parallel or nearly parallel). In some examples, due to themanufacturing tolerances, the alignment of the stretched axes 122 mayinclude for up to a 2° variance.

While optical film 100 may be described in some examples as having nomore than 1000 total (N) interference layers 102, it will be appreciatedthat the lower bound of the total number of layers (N) may be anysuitable amount configured to obtain the described optical properties.In some examples, there may be a trade-off between the obtained opticalproperties and the total number of layers (N)/thickness of the resultantfilm. For example, while in some examples the contrast ratio of a filmmay generally increase by increasing the total number of interferencelayers 102 included in optical film 100 absent any manufacturingcomplications as discussed prior, the thickness of the film will alsoincrease with the increasing number of layers. In some examples, such asin modern thin optical display devices, the overall thickness of a filmmay be a limiting factor as the availability for space in such opticaldisplay units is limited. In some examples, optical film 100 may providea significant increase in one or more optical properties (e.g., contrastratio), while having a significantly reduced film thickness (e.g., half)compared to other film constructions (e.g., the combined absorptionspolarizer and reflective polarized used in some conventional displayunits). In addition, excessive thickness of the film carries the risk ofdecreasing the overall contrast ratio due to depolarization of thepass-state light propagating through the film.

In some examples, optical film 100 may have between about 200 to about1000 total interference layers 102 with an overall thickness for opticalfilm 100 of less than about 100 μm including any optionalnon-interference or protective layers. In some examples, optical film100 may have a total thickness of less than about 100 μm (e.g., lessthan 60 μm) across all of the layers of optical film 100.

In some examples, the thickness of the individual interference layers102 may be relatively thin such that fewer than 30% of interferencelayers 102 have a thickness greater than about 200 nm (e.g., less than5% of interference layers 102 have a thickness greater than 200 nm orall interference layers 102 have a thickness less than about 200 nm),but may vary as function of position within optical film 100. Forexample, the thickness of the individual interference layers 102 mayvary such that the thickness of the individual interference layers 102generally increases (e.g., increasing thickens apart from localfluctuations) moving from the first layer number to the Nth layernumber. In some examples, optical film 100 may be characterized in termsof the film's thickness profile. For example, FIG. 3 is a plot of anexample thickness profile of optical film 100 that shows the relativethickness of the individual interference layers 102 as a function of thelayer number (e.g., layer number 1 to N plotted such that the thicknessof the layers generally increases from layer 1 to layer N). A fittedcurve 300 may be set to the region extending from the first layer to theNth layer (e.g., excluding any non-interference layers, spacer layers,or other optional optical layers that do not form part a stack/packet),with fitted curve 300 representing the best-fit regression applied to alayer thickness profile of optical film 100. In some examples, fittedcurve 300 may represent a 2^(nd), 3^(rd), 4^(th), or 5^(th) degreepolynomial regression analysis, an exponential regression analysis, orthe like.

As shown in FIG. 3, fitted curve 300 is represented as having an averageslope which represents the layer thickness profile of the individualinterference layers 102 of optical film 100 as a function of layernumber. In particular, the x-axis represents the layer number ofsequentially numbered interferences layers 102, numbered 1 to N and they-axis represents the average thickness (e.g., average thickness for theentire X-Y plane of FIG. 1) for a given layer number. As used herein,“sequentially numbered” interference layers 102 is used to refer to theinterference layers 102 numbered sequentially in a particular direction(e.g., moving along the Z-axis in FIG. 1). In some examples, theinterference layers 102 may be sequentially arranged to form a singlestack/packet as shown in FIG. 1. In other examples, the sequentiallynumbered interferences layers 102 may include one or more spacer layers(e.g., possibly thicker non-interference layers such as non-interferencelayer 408 described in FIG. 4 below) that do not function by opticalinterference and are not numbered as part of the sequentially numberedinterference layers 102. For example, in some examples, the sequentiallynumbered interference layers 102 numbered 1 to N may represent twostacks/packets of interference layers with each stack/packet includingsequentially arranged interference layers 102 separated by a spacerlayer (e.g., the first stack including layers 1 to m and the secondstack including layers (m+1) to N). As such the spacer layer is notcounted as a layer that makes up the thickness profile shown in FIG. 3.

In some non-limiting examples, slope of the fitted curve 300 may be apositive slope (e.g., greater than zero) and less than about 0.2 nm perlayer averaged across interference layers 102 sequentially numbered 1 toN of optical film 100, with N being greater than 200, with fewer than30% of interference layers 102 having a thickness greater than about 200nm. For example, fewer than 10% of interference layers 102 may have athickness greater than about 200 nm; in some examples, with fewer than5% of interference layers 102 may have a thickness greater than about200 nm; and in some examples, all of interference layers 102sequentially numbered 1 to N may have a thickness less than about 200nm.

In some non-limiting examples, optical film 100 may include Nsequentially numbered interference layers 102 where N is an integergreater than 200 and less than 1000 with each layer 102 having anaverage thickness of less than about 200 nm. In some such examples,fitted curve 300 representing a best-fit regression applied to thethickness profile plotting the respective thicknesses of the individualoptical layers 102 as a function of layer number, may define an averageslope as measured from the first layer to the Nth layer of less thanabout 0.2 nm/layer. In some such examples, due to the thickness profileof optical film 100, the film may define an average opticaltransmittance (T_(a)) of greater than about 85% for the firstpolarization state (a) and an average optical reflectance (T_(b)) ofgreater than about 80% for the orthogonal second polarization state (b)for normally incident light 110 within a predetermined wavelength range.

In some examples, slope may be substantially the same across allinterference layers 102 representing a continuous and constant change inthickness from layer to layer. In some such examples, the average slopemay be characterized as having a near constant step-change in layerthickness between adjacent interference layers 202. For example, ifslope is substantially constant at about 0.2 nm, layer number x may havea thickness of t nm while layer number (x+1) may have a thickness of(t+0.2 nm).

In some examples, the relative change in layer thicknesses betweenadjacent interference layers 102 may vary as a function of positionwithin optical film 100 such that the slope of fitted curve 300 may notbe substantially the same across all interference layers 102. In somesuch examples, the slope of fitted curve 300 may be characterized interms of a maximum and minimum slope. For example, optical film 100 mayinclude N sequentially numbered interference layers 102 where N is aninteger greater than 50 and less than 1000. Fitted curve 300,representing the best-fit regression may be applied to the thicknessprofile plotting the respective thicknesses of the individualinterference layers 102 as a function of layer number, may define bothmaximum slope and a minimum slope as a function of layer number. In somesuch examples, the difference between the maximum slope and the minimumslope may be less than about 0.70 nm/layer (e.g., less than about 0.57nm/layer) where the maximum and minimum slopes are each evaluated overany group of 25 to 50 adjacent interference layers 102. In some suchexamples, due to the thickness profile of optical film 100, the film maydefine an average optical transmittance (T_(a)) of greater than about80% for the first polarization state (a) and an average opticalreflectance (T_(b)) of greater than about 80% for the orthogonal secondpolarization state (b) for normally incident light 110 within apredetermined wavelength range.

In some examples, optical film 100 may be characterized by the ratiobetween the maximum difference between indices of refraction of theplurality of interference layers 102 (e.g., the maximum Δn_(x) betweeninterference layers 102 a and 102 b) versus the average slope of fittedcurve 300, e.g., Δn_(x)/K where K represents the average slope of fittedcurve 300. A lower average slope may improve the optical interferencebetween of optical film 100. In some examples, designing optical film100 to increase the Δn_(x)/K ratio such that it is relatively large(e.g., greater than 1) may result in a higher contrast ratio.

In some non-limiting examples, optical film 100 may define a Δn_(x)/Kgreater than about 1.2. In some such examples, optical film may definean optical density greater than about 1.4, greater than 1.6, greaterthan 1.8, greater than 2.0, or greater than about 3.0 for thepredetermined wavelength range. The “optical density” as used herein iscalculated as −log(T_(b)) averaged over a wavelength range of interest(e.g. 400 to 700 nm). In some examples, the higher the optical density,the high the contrast ratio will be for the optical film.

In some such examples, slope 302 of fitted curve 300 may represent theaverage slope across a subgroup of interference layers 102. For example,plurality of interference layers 102 may be divided into a plurality ofnon-overlapping groups of sequentially arranged interference layers 102within optical film 100. As used herein, “sequentially arranged”interference layers 102 means the interference layers are directlyadjacent to one another and do not include any spacer layers (e.g.,non-interference layer 408 described below in FIG. 4) disposed betweenany two adjacent interference layers 102 within a sequential arrangementof layers. For each group of sequentially arranged interference layers102, the layers may be sequentially numbered from one to m, with m beinggreater than 25, but less than N, with N representing the total numberof interference layers 102 (e.g., between 50 and 1000 layers) withinoptical film 100. Fitted curve 300 may be applied to the entirethickness profile of interference layers 102 as a function of the layernumber. The resultant average slope 302 (e.g. thickness change per mlayer numbers) may be determined for each subgroup of m layers. In somesuch examples, the maximum difference between the average slopes for allsubgroups (e.g., the difference between the maximum slope measured fromone group and the minimum slope measured from a different group) may beless than 0.70 nm/layer.

In view of the thickness profile of optical film 100, one willappreciate that the relative thicknesses of at least some of thedifferent interference layers 102 will differ throughout thestack/packet of interference layers 102 in optical film 100. In someexamples, the difference in thicknesses of plurality of interferencelayers 102 may be characterized by differences in the averagethicknesses of some of the interference layers 102. For example, opticalfilm 100 may include at least one interference layer 102 that defines anaverage thickness of less than about 50 nm (e.g., layer number 1), andthe average thickness of at least one other of the interference layers102 may be greater than about 100 nm (e.g., layer number N). In someexamples, optical film 100 may include at least two interference layers102 with a difference in average thicknesses of at least about 30% less(e.g., layer number 1 defines an average thickness that is at least 30%less than the average thickness of layer number N).

In some examples, the relative thickness of the interference layers 102may be described in terms of the optical thickness of a unit cell 106 a,106 b. As used herein, a “unit cell” is used to refer to a sequentiallyarranged pair of one HIR layer 102 a and one LIR layer 102 b and isreferred to in general as unit cell 106. Within FIG. 2, only tworespective unit cells 106 are shown (e.g., unit cell 106 a and unit cell106 b), however optical film 100 may include tens to hundreds of unitcells 106. In some examples, the unit cells 106 may be sequentiallyarranged or separated into different stacks/packets by one or morespacer layers.

The “optical thickness” (z) of a unit cell 106 may be defined as thethickness of the unit cell's respective HIR layer 102 a (d_(HIR)) timesthe refractive index of the HIR layer in the stretched direction (e.g.,n1_(x)) at the wavelength of interest plus the thickness of the cell'srespective LIR layer 102 b (d_(LIR)) times the refractive index of theLIR layer in the stretched direction (e.g., n2_(x)) at the samewavelength of interest. Each unit cell 106 may be sized such that theunit cell defines a respective optical thickness that is equal to aboutone half of a different respective central wavelength within thepredetermined wavelength range. For example, unit cell 106 a maycorrespond to central wavelength (λ_(a)), thereby defining an opticalthickness (τ_(a)) of (τ_(a)=λ_(a)/2=d_(HIR)*n1_(x)+d_(LIR)*n2_(x)). Eachrespective unit cell 106 within optical film 100 may correspond to adifferent central wavelength within the predetermined wavelength rangeto provide the desired transmission and reflection properties to thefilm over the predetermined wavelength range.

In some examples, the optical thickness (z) of unit cells 106 may becontrolled so that the intrinsic bandwidth of a given unit cell overlapswith the intrinsic bandwidth of the adjacent unit cells. By overlappingthe intrinsic bandwidths of adjacent unit cells 106, the constructiveinterference obtained by the interference layers 102 remains high. Oneway to improve the constructive interference obtained in optical film100 is to keep the difference in optical thicknesses (i) of adjacentunit cells 106 relatively small to produce a sufficient amount ofintrinsic bandwidth overlap. In some examples, the optical thickness (i)of unit cells 106 may be controlled such that less 10% of adjacent unitcells have a difference in optical thickness (z) that is more than 1%.For example, the optical film of Example 1 described further below, lessthan 6% of the adjacent unit cells had more than 1% difference inoptical thicknesses (z) and less than a 1.2% of the adjacent unit cellshad more than a 1.5% difference in optical thicknesses (z).

In some examples, the changes in optical thicknesses between adjacentunit cells (e.g. unit cell 106 a and unit cell 106 b) may be relativelysmall to obtain the desired optical properties. For example, in somenon-limiting examples, optical film 100 may include between about 100and about 400 sequentially arranged unit cells 106, each having one HIRlayer 102 a and one LIR layer 102 b that have a difference in indices ofrefraction (e.g., Δn_(x)) of at least about 0.24. Each unit cell 106defines a respective optical thickness (i) that is equal to about onehalf of a respective, and different, central wavelength (e.g., λ/2)within a predetermined wavelength range. In some such examples, for atleast 80% of pairs of adjacent unit cells (e.g., unit cell 106 a andunit cell 106 b form one pair 108 of adjacent unit cells), the ratio ofthe difference of the central wavelengths of the adjacent unit cells 106a, 106 b to an average of the central wavelengths of the adjacent unitcells 106 a, 106 b is less than about 2% (e.g.,abs([λ_(a(n))−λ_(a(n+1))]/[(λ_(a(n))−λ_(a(n+1)))/2])<2%).

In some examples, optical film 100 may be characterized in terms of anoptical power of interference layers 102. The “optical power” may bedefined as the integral of optical density in 1/(wavelength) spaceacross the region of interest for the blocked polarization state (b). Insome examples, a higher optical power may correspond to a highercontrast ratio in the region of interest. Depending on the intendedapplication for optical film 100, a certain amount of optical power forthe optical film may be desired. However, the optical power of perinterference layer generally will be inversely related to the totalnumber of interference layers such that the optical power per layer willdecrease with increasing total number of layers. As such, increasing thetotal number of interference layers while useful for obtaining otheroptical properties (e.g., sufficient coverage of a predeterminedwavelength range) may lead to a general decrease in the optical powerper layer. The optical films described herein may provide a higheroptical power per layer for, a given number of interference layers, thancapable of being obtained with conventional reflective polarizer films.

In some non-limiting examples, optical film 100 may include betweenabout 100 to about 1000 alternating HIR 102 a layers and LIR 102 blayers with each respective interference layer 102 reflecting ortransmitting light primarily by optical interference. In some suchexamples, optical film may define an optical power of optical film 100per interference layer 102 of greater than about (−0.0012*N+1.46), whereN represents the total number of interference layers 102 (e.g., N beingbetween about 100 to about 1000).

Additionally or alternatively, in some non-limiting examples, opticalfilm 100 may include at least 300 total alternating HIR 102 a layers andLIR 102 b layers with each respective interference layer 102 reflectingor transmitting light primarily by optical interference, such thatoptical film 100 defines an optical power per interference layer 102 ofgreater than about 0.7.

FIG. 15, described further below, shows the optical power per layerversus the number of layers for the non-limiting optical film of Example1 prepared in accordance with the disclosure. Also included in the plotof FIG. 15 are several comparative examples of conventional reflectivepolarizer films that are either commercially available or described inliterature (see Table 6). As shown in FIG. 15 and Table 6, the opticalfilm of Example 1 includes a total of 650 interference layers anddefines an optical power of approximately 0.74 per layer.

In some examples, plurality of interference layers 102 of optical film100 may be sequentially arranged such that each interference layer 102is directly adjacent to a neighboring interference layer to form anoptical stack/packet of at most 1000 individual layers. In otherexamples, optical film 100 may be separated into more than onestack/packet of interference layers 102 separated by a comparativelythick non-interference layer acting as a spacer layer (e.g., an opticallayer that does not reflect or transmit light primarily by opticalinterference). For example, FIG. 4A shows another example of opticalfilm 400 that can be formed to exhibit one or more of the opticalproperties described above with respect with optical film 100. As shownin FIG. 4A, optical film 400 includes a plurality interference layers402 separated into two optical stacks/packets 406 a, 406 b eachincluding a plurality of interference layers 402. Optical stacks/packets406 a, 406 b, are separated by a comparatively thick (e.g., thick incomparison to an individual interference layer 402) spacer layer 408.

As with optical film 100, optical film 400 may include tens to hundredsof interference layers 402 divided between optical stacks/packets 406 a,406 b. First optical stack/packet 406 a includes a total of (N_(a))interference layers 402 and second stack/packet 406 b includes a totalof (N_(b)) interference layers 402, such that optical film 400 includesa total of (N=N_(a)+N_(b)) sequentially numbered interference layers402.

Each interference layer 402 may be substantially the same as theinterference layers 102 described with respect to FIGS. 1 and 2. Forexample, interference layers 402 alternating HIR layers (e.g., similarto HIR layers 102 a) and LIR layers (e.g., similar to LIR layers 102 a).Additionally, as with optical film 100, in some examples, the totalnumber of interference layers 402 among optical stacks/packets 406 a,406 b of optical film 400 (e.g., N) may be less than 1000, or less than800 as described above.

In some examples, optical stacks/packets 406 a, 406 b may includesubstantially the same (e.g., the same or nearly the same) total numberof interference layers 402. For example, optical stacks/packets 406 a,406 b may independently include between about 50 and about 400interference layers 402 each, with the total number of interferencelayers 402 within each optical stack/packet 406 a, 406 b being the same(e.g., N_(a)=N_(b)). In some examples, the total number of interferencelayers 402 within a single optical stack/packet 406 a, 406 b may beabout 325 layers. In other examples, optical stacks/packets 406 a, 406 bmay include a different total number of interference layers 402 (e.g.,N_(a) N_(b)).

Spacer layer 408 may include any suitable optical material that does notreflect or transmit light primarily by optical interference (e.g., anon-interference layer). In some examples, spacer layer 408 may includepolyethylene naphthalate (PEN), copolymers containing PEN and polyesters(e.g., polyethylene terephthalate (PET) or dibenzoic acid), glycolmodified polyethylene terephthalate, polycarbonate (PC), or blends ofthese four classes of materials, or the like. In some examples, spacerlayer 408 may be formed by coextrusion or lamination thereby laminatingoptical stacks/packets 406 a, 406 b together with spacer layer 408 inbetween the two stacks/packets. Additionally or alternatively, spacerlayer 408 may be optically coupled to optical stacks/packets 406 a, 406b (e.g., adhered to the respective stack/packets 406 a, 406 b such thatlight transmits into and through spacer layer 408 without undergoing asignificant reflection or refraction).

Spacer layer 408 may be relatively thick compared to an individualinterference layer 402. For example, spacer layer 408 may have anaverage thickness greater than about 500 nm. Additionally oralternatively, spacer layer 408 may have an average thickness that is atleast 10 times the largest wavelength in the predetermined wavelengthrange. For example, if the predetermined wavelength range includesvisible light (e.g., about 400-700 nm), the thickness of spacer layer408 may be greater than 7,000 nm. In some examples, spacer layer 408 mayhave an average thickness that is at least 50 times the largestwavelength in the predetermined wavelength range. In some examples,spacer layer 408 may help reduce flow disturbances that might otherwiseoccur during the co-extrusion process of forming the multilayer opticalstacks/packets 406 a, 406 b.

In some examples, optical stacks/packets 406 a, 406 b may beindependently optimized to transmit or reflect light of differentpredetermined wavelength ranges. As such, optical film 400 may beconfigured to transmit and reflect light depending on its polarizationstate over multiple discreet wavelength ranges. For example, firstoptical stack/packet 406 a may be configured to transmit and reflectlight within the visible spectrum (e.g., about 400-700 nm) while secondoptical stack/packet 406 b may be configured to transmit and reflectlight within the near-infrared spectrum (e.g., about 800-1300 nm).

In some examples, the two optical stacks/packets 406 a, 406 b may beconfigured such that optical film 400 transmits and reflects lightdepending on its polarization state over a continuous predeterminedwavelength range (e.g., about 400-1300 nm). For example, opticalstacks/packets 406 a, 406 b may be configured such that thepredetermined wavelength ranges of the respective stacks/packets 406 a,406 b abut one another or overlap for a substantially continuous (e.g.,continuous or nearly continuous) predetermined wavelength range.

In some examples, first optical stack/packet 406 a may includesequentially arranged interference layers 402 numbered 1 to (N_(a)) ofalternating HIR and LIR layers configured to transmit or reflect lightof different polarization states within a first predetermined wavelengthrange. A pair so directly adjacent HIR and LIR interference layers 402may be characterized a unit cell 405, such that first opticalstack/packet 406 a has a total of about (M_(a)=N_(a)/2) unit cells 405.Likewise, second optical stack/packet 406 b may include sequentiallyarranged interference layers 402 numbered 1 to (N_(b)) of alternatingHIR and LIR layers, or about (M_(b)=N_(b)/2) unit cells 405, configuredto transmit or reflect light of different polarization states within asecond predetermined wavelength range. The respective HIR and LIRinterference layers 402 forming a respective unit cell 405 may becharacterized by the ratio between the average index of refraction forthe HIR layer to the average index of refraction for the LIR layer,e.g., (n1_(x)/n2_(x)).

In some examples, the index of refraction for the HIR (e.g., n1_(x)) andLIR (e.g., n2_(x)) interference layers 402 as well as the total numberof unit cells 405 (e.g., M) within a respective optical stack/packet 406may be selected such that the optical stack/packet exhibits a relativelyhigh contrast ratio (e.g., greater than 1000:1) for reflecting andtransmitting light within the predetermined wavelength range. In someexamples, the respective optical stack/packet 406 may be configured tofit the equation: [(n1_(x)/n2_(x))*M>300].

In some non-limiting examples, optical film 400 may include M_(a)sequentially arranged first unit cells 405 of alternating first HIR andsecond LIR interference layers 402. The first unit cells 405 may beoptimized to transmit or reflect light in a first predeterminedwavelength range (e.g., about 400-700 nm), but not a secondpredetermined wavelength range (e.g., about 800-1300 nm). In some suchexamples, the alternating first HIR and second LIR interference layers402 may define an average index of refraction of (n1_(x)) and (n2_(x))respectively such that the ratio of an average of indices of refractionof the first HIR layers (n1_(x)) to an average of indices of refractionof the second LIR layers (n2_(x)) times the total number of first unitcells 405 (M_(a)) is greater than about 300. Additionally, optical filmmay include M_(b) sequentially arranged second unit cells 405 ofalternating third HIR and forth LIR interference layers 402. The secondunit cells 405 may be optimized to transmit or reflect light in thesecond predetermined wavelength range (e.g., about 400-700 nm), but notthe first predetermined wavelength range (e.g., about 800-1300 nm). Thealternating third HIR and fourth LIR interference layers 402 may definean average index of refraction of (n3_(x)) and (n4_(x)) respectivelysuch that the ratio of an average of indices of refraction of the thirdHIR layers (n3_(x)) to an average of indices of refraction of the fourthLIR layers (n4_(x)) times the total number of second unit cells 405(M_(b)) is greater than about 300. In some such examples, light incidenton optical film 400 at any incidence angle less than about 30 degreeshaving any wavelength in the first and second predetermined wavelengthranges may undergo an average optical transmittance (e.g., T_(a)) for afirst polarization state (a) and an average optical transmittance (e.g.,T_(b)) for a second polarization state (b) such that a ratio of (T_(a))to (T_(b)) is greater than about 1000:1.

In some such examples, the multiple stack/packet 406 design of opticalfilm 400 may provide better a more efficient process for manufacturingthe film compared to, for example, an optical film that includes only asingle packet of interference layers configured to reflect and transmitlight within the same continuous predetermined wavelength range, dueimpart to the reduction in the total number of layers and complexity offorming a large single stack.

As with optical film 100, in some examples, the degree of transmittanceand reflectance of optical film 400 for substantially normally incidentlight 110 (e.g., normal or nearly normal to surface 404) within apredetermined wavelength range (e.g., visible light or about 400-700nm), may be characterized as having an average optical transmittance of(T_(a)) and optical reflectance of (R_(a)) for the first/passpolarization state (a) and an average optical transmittance of (T_(b))and optical reflectance of (R_(b)) for the second/reflect polarizationstate (a). The optical transmittance and reflectance values of opticalfilm 400 may be substantially similar to the values discussed above withrespect to optical film 100. For example, the average opticaltransmittance of (T_(a)) for optical film 400 may be greater than about80% for a first/pass polarization state (a), the average opticalreflectance (R_(b)) greater than about 80% for the orthogonalsecond/reflected polarization state (b), and the average opticaltransmittance (T_(b)) less than about 0.2% for the orthogonalsecond/reflected polarization state (b). In some examples, each opticalstack/packet 406 a, 406 b may be characterized as transmitting at least50% of normally incident light 110 having the first polarization state(a) in the predetermined wavelength range and reflecting at least 50% ofnormally incident light 110 in the second polarization state (b) withinthe predetermined wavelength range.

FIG. 4B is a plot of an example thickness profile for optical film 400that shows the thickness of each individual interference layer 402 as afunction of the layer number, wherein plurality of interference layers402 are sequentially numbered 1 to N, with N representing the totalnumber of interference layers 402 (e.g., N=N_(a)+N_(b)) in optical film400. As shown in FIG. 4B, spacer layer 408 is excluded from thethickness profile plot of optical film 400.

The thickness profile of optical film 400 may be characterized by twofitted curves 410, 412 each corresponding to the thickness profile of arespective optical stacks/packets 406 a, 406 b respectively. Fittedcurves 410, 412 represents the best-fit regression applied to a layerthickness profile of optical film 400 based on interference layers 402within the respective stack/packet. For example, fitted curve 410represents the thickness profile of first stack/packet 406 a,representing interference layers 402 sequentially numbered 1 to N_(a)and fitted curve 412 represents the thickness profile of secondstack/packet 406 a, representing interference layers 402 sequentiallynumbered (N_(a)+1) to (N_(a)+N_(b)) (e.g., corresponding to interferencelayers 402 sequentially numbered 1 to N_(b) of the second stack/packet406 b).

As shown in FIG. 4B each optical stack/packet 406 a and 406 b mayinclude a layer thickness profile (e.g., plotting individual layerthicknesses vs the layer number) that defines a respective slope. Insome examples, the average slopes for fitted curves 410, 412 may be lessthan 0.2 nm/layer number for interference layers 402 within a respectiveoptical stack/packet 406 a, 406 b. Each optical stack/packet 406 a, 406b of optical film 400 may include less than about 400 total interferencelayers 402 with each individual layer thicknesses of a respectiveinterference layers 402 being relatively thin (e.g., have an averagethickness less than about 200 nm).

In some examples, the average slope of fitted curves 410, 412 mayrepresent the average slope across a subgroup of interference layers 402within respective optical stack/packet 406 a, 406 b. For example,interference layers 402 within first optical stack/packet 406 a may bedivided into a plurality of non-overlapping groups of sequentiallyarranged interference layers 402. For each group of sequentiallyarranged interference layers 402, the layers may be sequentiallynumbered from one to m, with m being greater than N_(a)/10 but less thanN_(a), and with N_(a) representing the total number of interferencelayers 402 within first optical stack/packet 406 a. Fitted curve 410 maybe applied to the thickness profile for each group of layers as afunction of the layer number, with the resultant average slope for eachgroup (e.g. thickness change per m layer numbers) determined for eachgroup of layers. The maximum difference between the average slopes forall groups (e.g., the difference between the maximum slope measured fromone group and the minimum slope measured from a different group) may beless than 0.70 (e.g., less than 0.57 nm/layer) where the maximum slopeand the minimum slope are each evaluated over any group of 25 to 50adjacent layers.

In some examples, the layer thickness profile of optical film 400 may becharacterized by the best-fit linear equation applied to the thicknessprofiles of each optical stack/packet 406 a, 406 b as a function oflayer number. For example, FIG. 4C is a pair of plots of an examplethickness profile for optical film 400 that show the thickness of firstand second optical stacks/packets 406 a, 406 b as a function ofinterference layer number. As shown, first optical stack/packet 406 aincludes sequentially numbered interference layers 402 numbered 1 toN_(a) and second optical stack/packet 406 b includes sequentiallynumbered interference layers 402 numbered 1 to N_(b). A best-fit linearregression 420, 422 may be applied to each plot (e.g., linear leastsquares regression), to provide a respective average slope for eachassociated best-fit regression. In some examples, the maximum differencebetween the average slopes of best-fit linear regression 420, 422 forall optical stacks/packets 406 a, 406 b within optical film 400 may beless than about 20%. For example, as described below with respect to theoptical film of non-limiting Example 1 and FIG. 9, the slope of Packet 1and Packet 2 forming the optical film of Example 1 each exhibited anaverage slope of 0.17 nm/layer and 0.18 nm/layer respectively resultingin a difference in slopes of approximately 6%.

In some examples, first and second optical stacks/packets 406 a, 406 bmay include stitching within regions 424 and 426. Stitching describesthe optical design where at least two packets are present where there isonly a small amount of overlap between the reflected bands associatedwith each packet. This allows lower slopes to be used in the individualpackets which increases the optical power associated with each layer.FIG. 13 shows an example of a stitched layer design. In such examples,the change in layer thickness for layer of a respective opticalstacks/packets 406 a, 406 b adjacent to layer 408 (e.g., the first 30interference layers 402 adjacent to spacer layer 408 with in a givenstack/packet) may increase relative to the change in thickness/layer forthe other interference layers 402 within optical stack/packet 406 a, 406b. This change is shown in regions 424 and 426 of FIG. 4C as the layerthickness profile having a slight curl at the ends of the thicknessprofiles where the optical stack/packet 406 a, 406 b have neighboringsides against spacer layer 408.

In some non-limiting examples, optical film 400 may include plurality ofinterference layers 402 reflecting and transmitting light primarily byoptical interference, such that for a substantially normally incidentlight in a predetermined wavelength range, plurality of interferencelayers 402 transmit at least 80% of light having the first polarizationstate (e.g., T_(a)), reflect at least 80% of light having the orthogonalsecond polarization state (e.g., T_(b)). Plurality of interferencelayers 402 may be divided into a plurality of optical stacks/packets 406a, 406 b, with each pair of adjacent optical stacks/packets 406 a, 406 bseparated by one or more spacer layers 408 that does not reflect ortransmit light primarily by optical interference and each opticalstack/packet 406 a, 406 b transmitting at least 50% of light having thefirst polarization state (a) in the predetermined wavelength range andreflecting at least 50% of light having the second polarization state(b) in the predetermined wavelength range. Within each opticalstack/packet 406 a, 406 b interference layers 402 may be sequentiallynumbered (e.g., N_(a) or N_(b)), with each optical stack/packet 406 a,406 b having a best-fit linear equation (e.g., fitted lines 420, 422)correlating a thickness of the optical stack/packet 406 a, 406 b tointerference layer number, the linear equation having an average slope(e.g., stack thickness/layer number) in a region extending from thefirst interference layer 402 in the stack/packet to the lastinterference layer in the stack/packet (e.g., line 420 applied to layernumbers 1 to N_(a) of first optical stack/packet 406 a), a maximumdifference between the average slopes of the best-fit linear equationsof the plurality of optical stacks/packets 406 a, 406 b within opticalfilm 400 being less than about 20%. In some such examples, optical film400 may have an average optical density greater than about 2.5.

FIGS. 5A and 5B are a representative transmission plots for an exampleoptical film (e.g., optical film 400) in accordance with the disclosure,showing the transmission percentages for the first and secondpolarization states (e.g., the pass and reflected polarization statesrespectively) for normally incident light 110 within specifiedwavelength range 400-700 nm corresponding to the visible spectrum. FIG.5B shows the logarithmic plot for the transmission percentage for thesecond polarization state (b) (e.g., reflected polarization state). Therepresentative optical film 400 tested included two optical stacks(e.g., 406 a, 406 b) each having 325 interference layers 402 each withthe transmission spectrum measured for the first and second polarizationstates with a Lambda900 spectrometer (Perkin Elmer). As shown, theoverall second polarization state (b) transmission (e.g.,reflected-axis, T_(b)) across the visible spectrum range wassignificantly lower than 0.1%.

In some examples, optical films 100, 400 may include or be combined withone or more non-interference layers that may be used to separate and/orprotect one or more of the stack(s)/packet(s) of interference layers102, 402. For example, FIG. 6 shows another example of optical film 600that can be formed to exhibit one or more of the properties describedabove with respect with optical films 100, 400. As shown in FIG. 6optical film 600 includes a plurality interference layers 602 dividedinto two optical stacks/packets 606 a, 606 b laminated betweencomparatively thick non-interference layers 608. As shown in FIG. 6,first optical stack/packet 606 a is set between non-interference layers608 a and 608 b while second optical stack/packet 606 b is set betweennon-interference layers 608 c and 608 d such that non-interferencelayers 608 b and 608 c are directly adjacent to one another and act as aspacer layer between first and second optical stacks/packets 606 a. 606b. In some examples, due to their relative thickness, non-interferencelayers 608 a and 608 d external to optical stacks/packets 606 a, 606 bmay help protect the respective stack/packet from unintentional damage(e.g., scratching). In some examples, non-interference layers 608 a and608 b may define a reactive index of about 1.57.

Additionally or alternatively, one or more of non-interference layers608 may include coatings, such as hard coats (anti-scratching coating),diffusion coatings, anti-reflection coatings, or anti-glare coatings.

FIG. 7 is a diagram of an example display assembly 700 that includesreflective polarizer optical film 702, a liquid crystal display (LCD)assembly 710, and light source 720. As shown, LCD assembly 710 isilluminated by polarized light provided by the optical film 702 andlight source 720. LCD assembly 710 may include a multi-layer arrangementhaving an outer absorption polarizer film 712, one or more glass layers714, and a liquid crystal layer 716.

FIG. 7 depicts two types of light being transported through the displayassembly 700. Ambient light 730 represents light incident on displaysurface 711 that traverses through LCD assembly 710, the optical film702, and striking the diffuse reflective surface of light source 720where it is reflected back towards optical film 702. Light can alsooriginate from a backlight assembly of light source 720. For example,light source 720 may include an edge lit backlight that includes a lamp722 in a reflective lamp housing 724. Light from the lamp 722 is coupledto the light guide 726 where it propagates until it encounters a diffusereflective structure such as spot 728 (e.g., a discontinuous layer oftitanium oxide pigmented material). This discontinuous array of spots isarranged to extract lamp light and direct it toward the LCD assembly710. Ambient light 730 entering the light source 720 may strike a spotor it may escape from the light guide through the interstitial areasbetween spots. A diffusely reflective layer 729 (e.g., a layer oftitanium oxide pigmented material) may be positioned below the lightguide 726 to intercept and reflect such rays. In general, all the raysthat emerging from the light source 720 towards LCD assembly 710 may beillustrated as ray bundle 732. This ray bundle is incident on theoptical film 702 which transmits light having a first polarization statereferred to as “(a)” and effectively reflects light having theorthogonal polarization state (b). Optical film 702 may correspond toany of optical films 100, 400, 600 described above.

In some examples, LCD display assemblies may include an absorptionpolarizer film and reflective polarizer film (AP/RP films) between lightsource 720 and LCD assembly 710. In such examples, the AP film maytypically be used to create sufficient contrast for the display assemblywhile the inclusion of the RP film improves the brightness of the AP/RPfilm combination, particularly high ambient light environments or highglare conditions, compared to a system of only the AP film.Surprisingly, it has been found that the AP/RP films may be substitutedwith the high-contrast reflective polarizer (RP) optical film 702 asdescribed herein without any appreciable reduction in brightness orcontrast to display assembly 700 even in high ambient light environments(e.g., outside conditions). For example, while it was theorized thatincluding only the optical film 702 in display assembly 700 in absenceof a rear AP film would cause ambient light to undesirably reflect offoptical film 702 creating high levels of glare, in practice negligibleor relatively minor increases in glare were observed.

In some examples, display assembly 700 including optical film 702 mayexhibit an enhanced brightness of about 10%-15% compared to a comparabledisplay assembly that includes AP/RP films.

In some examples, display assembly 700 may include one or morebrightness enhancement films 740 disposed between light source 720 andoptical film 702 for increasing an axial brightness of the displayassembly 700. Example brightness enhancement films 740 may include, forexample, turning films, prism films, or the like.

In some non-limiting examples, display assembly 700 may include lightsource 720, LCD assembly 710 configured to be illuminated by lightsource 720, one or more brightness enhancement films 740 disposedbetween the light source 720 and LCD assembly 710 for increasing anaxial brightness of display assembly 700, and optical film 702 (e.g., anRP) disposed between one or more brightness enhancement films 740 andLCD assembly 710 and configured to substantially transmit light having afirst polarization state (a) and substantially reflect light having anorthogonal second polarization state (b). Optical film 702 may define anaverage optical transmittance less than about 0.2% for the secondpolarization state (e.g., T_(b)) with no absorbing polarizer (AP)disposed between light source 720 and LCD assembly 710. In some suchexamples, display assembly 700 may define a contrast ratio of at leasttwice that of a comparative display assembly having the sameconstruction except that the average transmittance of the RP of thecomparative display assembly for the second polarization state (b) isgreater than about 1.0%.

Additionally or alternatively, in some non-limiting examples, displayassembly 700 may include light source 720, LCD assembly 710 configuredto be illuminated by light source 720, one or more brightnessenhancement films 740 disposed between the light source 720 and LCDassembly 710 for increasing an axial brightness of display assembly 700,and optical film 702 (e.g., an RP) disposed between one or morebrightness enhancement films 740 and LCD assembly 710. Optical film 702may include a plurality of interference layers transmitting orreflecting light primarily by optical interference, such that for asubstantially normally incident light in a predetermined wavelengthrange, the plurality of the interference layers transmits at least 80%of light having a first polarization state (e.g., T_(a)) and transmitsless than about 0.2% of light having an orthogonal second polarizationstate (e.g., T_(b)), without an absorbing polarizer (AP) disposedbetween light source 720 and LCD assembly 710.

FIG. 8 is an example brightness profile for display assembly 700 thatincludes optical film 702 as a function of viewing angle compared to adisplay assembly with an AP/RP film. Curve 800 represents the brightnessprofile for display assembly 700 optical film 702 while curve 802represents the brightness profile for comparable display assemblyincluding an AP/RP film (e.g., APCF available from Nitto Denko Corp(Tokyo)). As shown optical film 702 provides a comparative viewingbrightness profile for normal viewing angle (e.g. ±20°) while providinga slight improvement in the brightness profile for off-axis viewingpositions. (e.g., >50°).

In some such examples, the use of optical film 702 as opposed totraditional AP/RP films may result in an overall thickness of the LCDdisplay assembly may be significantly reduced as high-contrast RPoptical films described herein may be formed at approximately half thethickness of a traditional AP/RP film. While using only optical film 702in display assembly 700 as opposed to an AP/RP film may result inbenefits associated with a reduction of the display assembly thickness,in some examples, an absorption polarizer film may be optionallyincluded between LCD assembly 710 and optical film 702 (not shown). Insome such examples, the absorption polarizer/optical film 702combination may provide improved brightness and/or contrast ratiocompared traditional AP/RP films.

In some examples, optical film 702 of display assembly 700 may performas a high-contrast RP to substantially transmit light having the firstpolarization state (a) and substantially reflect light having anorthogonal second polarization stated (b). In some examples, opticalfilm 702 may define an average optical transmittance less than about0.2% for the second polarization state (b), wherein no absorbingpolarizer is disposed between light source 720 and the liquid crystallayer 716, and wherein a contrast ratio of display assembly 700 is atleast twice that of a comparative display assembly having the sameconstruction except that the average transmittance of the reflectivepolarizer of the comparative display assembly for the secondpolarization state is greater than about 1.0%.

In some examples, one or more of the optical films 100, 200, 400, 600described herein may be incorporated into an optical system designed fordisplaying an object to a viewer centered on an optical axis (e.g.,virtual reality display systems). Such optical systems may include oneor more optical lenses having a non-zero optical power with a reflectivepolarizer (e.g., optical film 100, 200, 400, 600) disposed on andconforming to a first major surface of the one or more optical lensesand a partial reflector disposed on and conforming to a second majorsurface of the one or more optical lenses. In some examples, the lensand reflective polarizer may be convex about one or two orthogonal axesand disposed between a stop surface (e.g., an exit pupil or an entrancepupil) and an image surface (e.g., a surface of a display panel or asurface of an image recorder) to produce a system having a high field ofview, a high contrast, a low chromatic aberration, a low distortion,and/or a high efficiency in a compact configuration that is useful invarious devices including head-mounted displays, such as virtual realitydisplays, and cameras, such as cameras included in a cell phone, forexample.

FIG. 10 is a schematic cross-sectional view of an example optical system1000 (e.g., a virtual reality display system) that includes an imagesurface 1030, a stop surface 1035, and an optical stack 1010 disposedbetween the image surface 1030 and the stop surface 1035. An x-y-zcoordinate system is provided in FIG. 10. Image surface 1030 may be anoutput surface of an image forming device such as a display panel thatemits polarized or unpolarized light, while stop surface 1035 may be anexit pupil of optical system 1000 and may be adapted to overlap anentrance pupil of a second optical system, which may be a viewer's eyeor a camera, for example.

In some examples, optical stack 1010 may include optical lens 1012having first and second major surfaces 1014 and 1016, a reflectivepolarizer 1027 (e.g. optical film 100, 200, 400, 600) disposed on firstmajor surface 1014, and a partial reflector 1017 disposed on secondmajor surface 1016 of optical lens 1012. In some examples, optical stack1010 may also include one or more quarter wave retarders 1015, 1025disposed on respective first and second major surface 1014 and 1016.

As shown in FIG. 10, optical stack 1010 may be convex toward the imagesurface 1030 along orthogonal a first and/or a second axes (e.g., the x-and y-axes, respectively). Optical stack 1010 can be made by firstforming reflective polarizer 1027 with an optional first quarter waveretarder 1025 coated or laminated to reflective polarizer 1027 and thenthermoforming the resulting film into a desired shape to correspond tooptical lens 1012. Partial reflector 1017 and optional second quarterwave retarder 1015 may be prepared by coating a quarter wave retarderonto a partial reflector film, by coating a partial reflector coatingonto a quarter wave retarder film, by laminating a partial reflectorfilm and a quarter wave retarder film together, or by first forming lens1012 (which may be formed on a film that includes reflective polarizer1027) in a film insert molding process and then coating the partialreflector 1017 on the second major surface 1016. In some examples, lens1012 may be formed by injection molding lens 1012 between first andsecond films of the reflective polarizer 1027 and partial reflector1017. The first and second films may be thermoformed prior to theinjection molding step.

Image source 1031 includes the image surface 1030 and stop surface 1035is an exit pupil for optical system 1000. In some examples, image source1031 may be a display panel. In other examples, a display panel may notbe present and, instead, image surface 1030 is an aperture adapted toreceive light reflected from objects external to optical system 1000.

In some examples, a second optical system 1033 having an entrance pupil1034 may be disposed proximate optical system 1000 with stop surface1035 overlapping entrance pupil 1034. The second optical system 1033 maybe a camera, for example, adapted to record images transmitted throughimage surface 637. In some examples, second optical system 1033 is aviewer's eye and entrance pupil 1034 is the pupil of the viewer's eye.In such examples, optical system 1000 may be adapted for use in ahead-mounted display.

Reflective polarizer 1027 may be any one of optical films 100, 200, 400,600 described herein. For example, reflective polarizer may include atleast 50 sequentially numbered interference layers, each layer may berelatively thin (e.g., have an average thickness less than about 200 nm)where a fitted curve being a best-fit regression applied to a layerthickness profile reflective polarizer 1027 as a function of layernumber, (e.g., curve 300 of FIG. 3), an average slope of the fittedcurve in a region extending from the first layer to the Nth layer beingless than about 0.2 nm/layer. Reflective polarizer 1027 substantiallytransmits light having a first polarization state (a) (e.g., linearlypolarized in a first direction) and substantially reflects light havingan orthogonal second polarization state (b) (e.g., linear polarized in asecond direction orthogonal to the first direction).

Partial reflector 1017 has an average optical reflectance of at least30% and optical transmission of at least 30% in the predeterminedwavelength range, which may be any of the wavelength ranges describedelsewhere herein. Any suitable partial reflector may be used. In someexamples, partial reflector 1017 may be a half mirror, for example. Insome examples, partial reflector 1017 may be constructed by coating athin layer of a metal (e.g., silver or aluminum) on a transparentsubstrate. Additionally or alternatively, partial reflector 1017 mayalso be formed by depositing thin-film dielectric coatings onto asurface of a lens, or by depositing a combination of metallic anddielectric coatings on the surface of the lens, for example. In someexamples, partial reflector 1017 may itself be a reflective polarizer.

The optional first and second quarter wave retarders 1015, 1025 may be acoating or film formed from any suitable material including, forexample, linear photopolymerizable polymer (LPP) materials and theliquid crystal polymer (LCP) materials described in US Pat. App. Pub.Nos. US 2002/0180916 (Schadt et al.), US 2003/028048 (Cherkaoui et al.)and US 2005/0072959 (Moia et al.). Suitable LPP materials includeROP-131 EXP 306 LPP and suitable LCP materials include ROF-5185 EXP 410LCP, both available from Rolic Technologies, Allschwil, Switzerland. Insome examples, quarter wave retarders 1015, 1025 may be quarter waveretarders at at least one wavelength in the predetermined wavelengthrange.

During operation of optical system 1000, light rays 1037 and 1038 areeach transmitted through the image surface 1030 and the stop surface1035. Light rays 1037 and 1038 may each be transmitted from the imagesurface 1030 to the stop surface 1035 (in head-mounted displayapplications, for example), or light rays 1037 and 1038 may betransmitted from the stop surface 1035, to the image surface 1030 (incamera applications, for example). Light ray 1038 may be a central lightray whose optical path defines a folded optical axis 1040 for opticalsystem 1000, which may be centered on the folded optical axis 1040.Light ray 1038 may pass through optical stack 1010 without significantdeviation from optical axis 1040.

The path of light ray 1037 may be deflected due to optical stack 1010.Light ray 1037 is transmitted through partial reflector 1017 (includingoptional second quarter wave retarder 1015) into and through lens 1012.After making a first pass through lens 1012, the light ray passesthrough optional first quarter wave retarder 1025 and reflects fromreflective polarizer 1027. In examples where two quarter wave retarders1015, 1025 are incorporated into optical stack 1010, the quarter waverestarters 1015, 1025 may disposed both sides of lens 1012 such that thequarter wave retarders 1015, 1025 lie between reflective polarizer 1027and image source 1031. In some such examples, image source 1031 may beadapted to emit light having a polarization along the pass axis (a) forreflective polarizer 1027 so that after passing through the quarter waveretarder 1015, 1025 the light becomes polarized along the block axis forthe reflective polarizer 1027 and therefore reflects from the reflectivepolarizer 1027 when it is first incident on the film. After light ray1037 initially reflects from reflective polarizer 1027, it passes backthrough the first quarter wave retarder 1025 and is then reflected frompartial reflector 1017 (other light rays not illustrated are transmittedthrough partial reflector 1017) back through lens 1012 and first quarterwave retarder 1025 and is then again incident on the reflectivepolarizer 1027. After passing through first quarter wave retarder 1025,reflecting from partial reflector 1017 and passing back through firstquarter wave retarder 1025, light ray 1037 has a polarization along thepass axis (a) for reflective polarizer 1027. Light ray 1037 is thereforetransmitted through reflective polarizer 1027 and is then transmittedthrough stop surface 1035 into second optical system 1033.

The design of the single integrated optical stack 1010 may provide ahigh field of view in a compact system. Light ray 1037, which istransmitted through an outer edge of image surface 1030, is a chief raythat intersects stop surface 1035 at the folded optical axis 1040 with aview angle of θ, which may be at least 40 degrees, at least 45 degrees,or at least 50 degrees, for example. The field of view at the stopsurface 1035 is 20, which may be at least 80 degrees, at least 90degrees, or at least 100 degrees, for example.

In some non-limiting examples, optical system 1000 may include one ormore optical lenses 1012 having a non-zero optical power, reflectivepolarizer 1027 disposed on and conforming to a first major surface 1014of one or more optical lenses 1012, and partial reflector 1017 disposedon and conforming to a different second major surface 1016 of the one ormore optical lenses 1012. Reflective polarizer 1027 may substantiallytransmit light 1037 having a first polarization state (a) andsubstantially reflecting light having an orthogonal second polarizationstate (b) with partial reflector 1017 having an average opticalreflectance of at least 30% for a predetermined wavelength range, suchthat an average optical transmittance of optical system 1000 for anincident light 1037 along the optical axis 1040 having the secondpolarization state (b) is less than about 0.1%.

Additional examples of optical systems for displaying an object to aviewer centered on an optical axis that include one or more reflectivepolarizers are disclosed and described in U.S. patent application Ser.No. 14/865,017, which is incorporated herein by reference in itsentirety. One or more of the optical films 100, 200, 400, 600 describedherein can be used in such systems as the reflective polarizersdescribed therein.

In some examples, one or more of the optical films 100, 200, 400, 600described herein may be incorporated as the reflective polarizer in apolarizing beam splitter (PBS). A PBS may be used to effectively splitunpolarized light into two polarized states. PBS systems may be used insemiconductor, photonics instrumentation, or other optical systems tosubstantially transmit light in a first polarization state (a) whilesubstantially reflecting polarized light in a second orthogonalpolarization state (b). In some examples, the PBS systems may bedesigned receive light at a 0° or 45° angle of incidence while splittingoutput polarized beams at about a 90° of separation.

FIG. 11 is a schematic cross-sectional view of an example PBS 1100 thatincludes a first prism 1102, a second prism 1104, a reflective polarizer1110, and light source 1150. First prism 1102 includes input face 1112for receiving incident light from light source 1150, output face 1114and first hypotenuse 1116. In some examples, input face 1112 and outputfaces 114 may be further shaped to have an active area for receiving andtransmitting light passing through first prism 1102. Second prism 1104includes an output surface 1118 and second hypotenuse 1120.

Reflective polarizer 1110 is disposed between first and secondhypotenuses 1116 and 1120 of the respective first and second prisms 1102and 1104. Reflective polarizer 1110 may include any of the optical films100, 200, 400, 600 describe herein. For example, reflective polarizer1110 may include at least 50 sequentially numbered interference layers,each layer may be relatively thin (e.g., have an average thickness lessthan about 200 nm) where a fitted curve being a best-fit regressionapplied to a layer thickness profile reflective polarizer 1110 as afunction of layer number, (e.g., curve 300 of FIG. 3), an average slopeof the fitted curve in a region extending from the first layer to theNth layer being less than about 0.2 nm/layer.

First and second prisms 1102, 1104 may include glass or polymericmaterials. Suitable polymeric materials for first and second prisms1102, 1104 include, for example, transparent optical polymers such asacrylic polymers (e.g., polymethylmethacrylates), cyclic-olefincopolymers, polycarbonates, and combinations thereof. In some examples,first and second prisms 1102, 1104 may be formed by injection moldingusing thermoplastic acrylic polymers such as acrylic polymerscommercially available under the trade designation “OPTOREZ OZ-1330”Series polymers from Hitachi Chemical Company, Ltd, Tokyo, Japan. Insome examples, it may desirable to form first and second prisms 1102,1104 using the same polymeric materials to reduce optical variationsbetween the two prisms, however in other examples first and secondprisms 1102, 1104 may be formed with different materials. In someexamples, first and second prisms 1102, 1104 may be similarly sizedwhile in other examples, first prism 1102 may have a volume that is lessthan the volume of second prism 1104. In some examples, the volume offirst prism 1102 may be no greater than about half (or no greater thanabout 60 percent, or no greater than about 40 percent) of the volume ofthe second prism 1104. The selection of which portions of first prism1102 that may be removed may depend in part on the optical paths of theincidence, transmitted, and reflected light originating within envelop1152.

During operation, light source 1150 produces a light beam having anenvelope 1152 that includes central light ray 1154. Light from lightsource 1150 may be non-polarized having a predetermined wavelengthrange. Central light ray 1154 enters first prism 1102 through inputsurface 1112 where it then transmits through the prism and becomesincident on reflective polarizer 1110 at an incidence angle of about45°. At such point, central light ray 1154 then transmits through andreflects off reflective polarizer 1110 in accordance to the polarizationstate of the light. For example, light corresponding to the firstpolarization state (a) (e.g., the pass-state) passes through reflectivepolarizer 1110 and continues through second prism 1104 as transmittedlight ray 1156 having first polarization state (a) where it reachesoutput surface 1118. Light corresponding to the second orthogonalpolarization state (b) (e.g., the block/reflect) will reflect off thereflective polarizer 1110 as reflected light ray 1158 having secondorthogonal polarization state (b). Due to the angle of incidence betweenlight ray 1154 and reflective polarizer 1110, reflected light ray 1158with will reflect off reflective polarizer 1110 in the direction ofoutput face 1114. In some examples, transmitted light ray 1156 andreflected light ray 1158 will progress at 90° to one another.

PBS 1100 may include additional components (not shown) attached to oneor more of the output or other faces of first and second prisms 1102,1104. Additionally or alternatively, PBS 1100 may be incorporated indifferent optical systems. The various components or PBS 1100 or thosecomponents attached to PBS 1100 could be in direct contact or attachedthrough an optically clear adhesive. In some examples, reflectivepolarizer 1110 is attached to one or both of first and second prisms1102, 1104 using optically clear adhesive layers. Additional examples ofPBS designs and optical systems incorporating PBS systems are disclosedand described in U.S. patent application Ser. No. 14/865,017, which isincorporated herein by reference in its entirety.

In some non-limiting examples, PBS 1100 may include first and secondprisms 1102, 1104 and reflective polarizer 1110 disposed between andadhered to first and second prisms 1102, 1104 (e.g., along first andsecond hypotenuses 1116, 1120). In such examples, reflective polarizer1110 may substantially reflect polarized light having a firstpolarization state (a) and substantially transmit polarized light havingan orthogonal second polarization state (b), such that when incidentlight (e.g., light ray 1154) having a predetermined wavelength entersPBS 1100 from input face 1112 of PBS 1100 and exits through an outputface of PBS 1110 (e.g., output face 1118 or 1114) after encounteringreflective polarizer 1110 at least once, a ratio of an average intensityof the exiting light (e.g., transmitted light ray 1156 or reflectedlight ray 1158) to an average intensity of the incident light (e.g.,light ray 1154) is greater than about 90% when the incident light hasthe first polarization state (a), and less than about 0.2% when theincident light has the second polarization state (b).

EXAMPLES Example 1

A birefringent reflective polarizer optical film was prepared asfollows. Two multilayer optical packets were co-extruded with eachpacket comprised of 325 alternating layers of polyethylene naphthalate(PEN) and a low index isotropic layer, which was made with a blend ofpolycarbonate and copolyesters (PC:coPET) such that the index is about1.57 and remains substantially isotropic upon uniaxial orientation,wherein the PC:coPET molar ratio is approximately 42.5 mol % PC and 57.5mol % coPET and has a Tg of 105 degrees centigrade. This isotropicmaterial was chosen such that after stretching its refractive indices inthe two non-stretch directions remains substantially matched with thoseof the birefringent material in the non-stretching direction while inthe stretching direction there is a substantial mis-match in refractiveindices between birefringent and non-birefringent layers. The PEN andPC/coPET polymers were fed from separate extruders to a multilayercoextrusion feedblock, in which they were assembled into packets of 325alternating optical layers (“Packet 1” and “Packet 2” respectively),plus a thicker protective boundary layer of the PC/coPET, on the outsideof the stacked optical packets, for a total of 652 layers.

This layer profile for the high contrast reflective polarizer (HCRP)optical film of Example 1 is shown in FIG. 9 with Packets 1 and 2indicated. The average slope of Packet 1 was about approximately 0.17nm/layer and the average slope of Packet 2 was approximately 0.18nm/layer using a least squares linear regression, exhibiting adifference in the respective slopes for the two packets of approximately6%. The film of Example 1 had a resulting total thickness as measured bya capacitance gauge of approximately 63.2 μm.

To assess the alignment of the plurality of interference layers ofExample 1, the optical axis of the film was determined for linearlypolarized light incident on each respective major surface of the film.The optical axis of a film corresponds to the orientation of incomingpolarized light within the plane of the film that allows the minimumamount of linearly polarized light to pass through the film (e.g.,aligned with stretch axis 120 of FIG. 2). In an ideal scenario, theoptical axis of the film would be the same regardless of the surfacethat the polarized light enters the film. However, due to variations inthe manufacturing process or misalignment of the individual optical axesof the plurality of interference layers, the optical axis of the filmmay be dependent on which surface the polarized light enters. In someexamples, the greater the degree of misalignment between the pluralityof layers, the greater the difference of the optical axes may be for thefilm. The difference between the optical axes of the film for the twosurfaces may, in some examples, be used as a metric for assessing thealignment between the plurality of interference layers. The two opticalaxes for the film of Example 1 was measured for the two surfaces usinglinearly polarized light. The polarized light was projected directly atthe first major surface of the film and the film was rotated until theminimum amount of the polarized light passed through the film. Theoptical axis for the first major surface was then marked as beingparallel to the polarization axis of the polarized light. The processwas repeated for the second major surface of the film. The differencebetween the optical axes for the first major surface and the secondmajor surface for the film of Example 1 was determined as less than 0.1degrees indicating strong alignment among the plurality of interferencelayers.

Example 2

A birefringent reflective polarizer optical film was made with the sameprocess conditions as the Film of Example 1 except the optical film wasmade to an overall thickness of approximately 66.7 μm as measured by acapacitance gauge.

Example 3

A birefringent reflective polarizer optical film was prepared asfollows. Two multilayer optical packets were co-extruded with eachoptical packet comprised of 325 alternating layers of 90/10 coPEN (e.g.,90 mol % polyethylene naphthalate (PEN) and 10 mol % polyethyleneterephthalate (PET)) and a low index isotropic layer of PC/coPET asdescribed above in Example 1. The 90/10 coPEN and PC/coPET polymers werefed from separate extruders to a multilayer coextrusion feedblock, inwhich they were assembled into packets of 325 alternating opticallayers, plus a thicker protective boundary layer of the PC:coPET, on theoutside of the stacked optical packets, for a total of 652 layers. Thisfilm had a resulting physical total thickness as measured by acapacitance gauge of approximately 63.2 μm.

Table 1 below provides comparative average transmission profiles for thefirst and second polarization states (a) and (b) (e.g., pass-axis andblock-axis) across the visible spectrum range of 450-650 nm for theoptical films of Examples 1-3, compared to commercially availableabsorption polarizer (AP) and reflective polarizers (RP), and thosereferenced in literature.

TABLE 1 Contrast Optical Film Sample T_(a) (%) T_(b) (%) Ratio DensityExample AP 85.1 0.007 13,092:1    4.16 Example commercial RP 1 89.94.633 26:1 1.40 (3M, St. Paul, MN) Example commercial RP 2 87.6 4.98821:1 1.34 (3M, St. Paul, MN) Example commercial RP 3 87.7 2.020 50:11.73 (3M, St. Paul, MN) Example literature RP 90.4 2.035 48:1 1.71Example 1 (HCRP) 90.0 0.015 11,207:1    3.97 Example 2 (HCRP) 90.0 0.0694,060:1   3.49 Example 3 (HCRP) 89.5 0.059 2,659:1   3.37

Table 2 below represents the transmission and reflectance values in thefirst polarization state (a) and orthogonal second polarization state(b) calculated for Example films 1-3 based on the values in Table 1. Thevalues are calculated assuming negligible loss of light energyassociated with absorption by the film layers.

TABLE 2 Δn_(x) Film Sample T_(a) (%) T_(b) (%) R_(a) (%) R_(b) (%)T_(b)/R_(b) R_(a)/T_(a) (n1_(x) − n2_(x)) * (n1_(x):n2_(x)) * Example 190 0.015 10 99.985 0.00015 0.11111 0.25 1.16 (HCRP) Example 2 90 0.06910 99.931 0.00069 0.11111 0.25 1.16 (HCRP) Example 3 89.5 0.059 10.599.941 0.00059 0.11732 0.25 1.16 (HCRP) * Determined for 633 nm

FIG. 12 is a plot of example thickness profiles (layer thickness vslayer number) for example reflective polarizer films as described herecompared to conventional reflective polarizers. The films are describedbelow in Table 3. Films 1206 and 1208 represent commercially availablemultilayer reflective polarizer films available from 3M, Saint Paul,Minn. Film 1210 is a representative conventional polarizer film having275 layers with a maximum to minimum thickness ratio of 2.2 where thethickness continuously varies as described in that patent. Lines 1202and 1204 correspond to the first and second optical stacks/packetsrespectively of HCPR Example 1. The layer thickness profiles weremeasured using an Atomic Force Microscope (AFM).

TABLE 3 Average Optical Slope Density Avg Film Sample (nm/layer)(450-650 nm) Example 1 (HCRP) (Packet 1 - 1202) 0.18 3.37 Example 1(HCRP) (Packet 2 - 1204) 0.17 3.37 Example commercial RP 2 0.226 1.40(3M, St. Paul, MN) - Film 1208 Example commercial RP 3 0.211 1.73 (3M,St. Paul, MN) - Film 1206 Example conventional RP - Film 1210 0.24 1.83

Table 4 below represents the calculated difference between the highestslope region and the lowest slope region for each of films/packets1202-1208 shown in FIG. 12. The respective slope for a give region wasdetermined using a least squares linear regression over a range of 25layers.

TABLE 4 Difference between max and Film Sample min slopes (nm/layer)Example 1 (HCRP) (Packet 1 - 1202) 0.48 Example 1 (HCRP) (Packet 2 -1204) 0.24 Example commercial RP 2 (3M, St. 1.47 Paul, MN) - Film 1208Example commercial RP 3 (3M, St. 0.75 Paul, MN) - Film 1206

Example 4

An optical film was produced using a similar manufacturing processes asdescribed with respect to Examples 1, 2, and 3. An alternate layerthickness profile was implemented that utilized a lower slope/layerprofile than that of Examples 1, 2, and 3. In particular, two multilayeroptical stacks/packets were co-extruded with each containing 325alternating layers of HIR layer of polyethylene naphthalate (PEN) and aLIR isotropic layer which was made with a blend of 20 wt % PETg (EastmanChemicals, Knoxville, Tenn.) and 80 wt % Xylex (Sabic, Houston, Tex.),an alloy of polycarbonate and copolyester. The refractive index of theLIR layer was approximately 1.57 and remained substantially isotropicupon uniaxial orientation. This isotropic material was chosen such thatafter stretching its refractive index in the stretched directionremained substantially unchanged and similar to that of the refractiveindex of the HIR layer in the non-stretched direction, while therefractive index of the HIR layer in the stretched direction had asubstantial mismatch to the refractive index LIR layer in the samedirection. The materials for the HIR and LIR layers were fed fromseparate extruders supplying a multilayer coextrusion feedblock in whichthey were assembled into two packets of 325 alternating optical layers,plus a thicker protective boundary layer of the isotropic LIR materialon each side of each packet, for a total of 653 layers, where the spacerlayers between the stacked optical packet optically and mechanically isconsidered a single layer. The first packet (e.g., “Packet 1”) wascomposed of relatively thin alternating HIR/LIR layers while the secondpacket (e.g., “Packet 2”) composed of relatively thick alternatingHIR/LIR layers to correspond to predetermined wavelength ranges ofapproximately 390 nm to 620 nm and 600 nm to 900 nm respectively. Thefilm was stretched in a parabolic tenter as described in U.S. Pat. No.6,916,440 which is incorporated by reference in its entirety. The filmwas stretched at a temperature of approximately 316° F. (e.g., 158° C.).The film was stretched at approximately a 6:1 ratio in the transversedirection and approximately a 0.46:1 ratio in the machine direction,that is the film is relaxed in the machine direction.

FIG. 13 shows a plot of the layer thickness profile for the optical filmof Example 4 obtained by AFM. The average slope of Packet 1 wascalculated at approximately 0.104 nm/layer and the average slope ofPacket 2 was calculated at approximately 0.141 nm/layer using a leastsquares linear regression. The film of Example 4 had a resulting totalthickness as measured by a capacitance gauge of approximately 65.7 μm.The average pass state transmission (T_(a)) was approximately 89.1% andthe average block/reflected state transmission (T_(b)) was approximately0.057% evaluated over the wavelength range of 450-650 nm.

FIG. 14 shows a plot of the block state transmission (T_(b)) for thefilm of Example 4 over the wavelength range of 375-850 nm.

Example 5

Table 5 below shows the Δn_(x)/K ratio for the optical films of Examples1 and 4 described above compared to Example commercial RP 2 and RP 3. Asshown, each respective packet of the optical films of Examples 1 and 4show a Δn_(x)/K ratio of greater than 1.2 while the Example commercialRP 2 and RP 3 have a Δn_(x)/K ratio of less than 1.

TABLE 5 Film Sample Δn_(x) K Δn_(x)/K Example 1 (HCRP) (Packet 1) 0.250.172 1.45 Example 1 (HCRP) (Packet 2) 0.25 0.177 1.41 Example 4 (HCRP)(1^(st) Packet) 0.25 0.141 1.77 Example 4 (HCRP) (2^(nd) Packet) 0.250.103 2.43 Example commercial RP 2 0.22 0.227 0.97 (3M, St. Paul, MN)Example commercial RP 3 0.2 0.247 0.81 (3M, St. Paul, MN)

Example 6

Table 5 below shows the optical density, optical power, and otheroptical properties for the optical film of Example 1. Also included inTable 5, are the results obtained for twenty four comparative samples ofconventional reflective polarizer films. The comparative samplescorrespond to various polarizer films obtained either commercially orprepared using techniques disclosed in literature. The optical power perlayer versus the total number of layers for the films listed in Table 6are plotted in FIG. 15. As shown in FIG. 15, the optical film ofExamples 1 and 4 each exhibit an optical power per layer greater than(−0.0012*N+1.46) (designated by line).

TABLE 6 Total Optical Left Band Right Band Optical Optical Film SampleLayers T_(a) (%) T_(b) (%) Density Edge (nm) Edge (nm) Power Power/layerExample 1 650 90.5 0.02 3.70 420 924 480 0.74 (HCRP) Example 4 650 90.10.01 3.90 420 924 509 0.78 (HCRP) Comparative 274 32 0.5 2.30 420 924299 1.09 Sample 1 Comparative 275 36 1.4 1.85 420 924 241 0.88 Sample 2Comparative 275 90 1 2.00 420 924 260 0.94 Sample 3 Comparative 825 890.5 2.30 420 924 299 0.36 Sample 4 Comparative 550 89.9 0.4 2.40 420 924311 0.57 Sample 5 Comparative 550 89.7 0.4 2.40 420 924 311 0.57 Sample6 Comparative 550 89.9 0.5 2.30 420 924 299 0.54 Sample 7 Comparative550 89.9 0.4 2.40 420 924 311 0.57 Sample 8 Comparative 825 89.9 0.22.70 420 924 351 0.42 Sample 9 Comparative 550 89.9 0.4 2.40 420 924 3110.57 Sample 10 Comparative 275 89.2 1 2.00 420 924 260 0.94 Sample 11Comparative 275 89.2 0.5 2.30 420 924 299 1.09 Sample 12 Comparative 27589.2 1 2.00 420 924 260 0.94 Sample 13 Comparative 550 89.2 0.7 2.15 420924 280 0.51 Sample 14 Comparative 550 89.8 0.5 2.30 420 924 299 0.54Sample 15 Comparative 550 89.8 0.4 2.40 420 924 311 0.57 Sample 16Comparative 550 90.3 0.2 2.70 420 924 351 0.64 Sample 17 Comparative 55089.2 0.3 2.52 420 924 328 0.60 Sample 18 Comparative 550 89.2 0.4 2.40420 924 311 0.57 Sample 19 Comparative 550 89.2 0.7 2.15 420 924 2800.51 Sample 20 Comparative 550 89.2 0.7 2.15 420 924 280 0.51 Sample 21Comparative 825 89.2 0.5 2.30 420 924 299 0.36 Sample 22 Comparative 27589.2 0.9 2.05 420 924 266 0.97 Sample 23 Comparative 275 89.2 1 2.00 420924 260 0.94 Sample 24

Example 7

A comparative display assembly study was performed using the LCD displayof an iPad4 (Apple Computer, Cuppertino, Calif.). Three reflectivepolarizers were tested in the display assembly as the rear reflectivepolarizer (e.g., position of optical film 702 in display assembly 700).The reflective polarizer tested included the stock RP film of the iPad4laminated to a polyvinyl alcohol type of adsorbing polarizer(“Comparative AP/RP film”); the stock RP film of the iPad4 without thepresence of the RP (“Comparative RP film”); and the high contrastreflective polarizer optical film of Example 1. The bonding adhesiveused to adhere the polarizer optical films to the LCD display was clearOCA 8171 available from 3M Company, St. Paul, Minn. The light sourceused for the testing was the stock backlight with brightness enhancementfilms (e.g., prism film/prism film/diffuser sheet) provided with theiPad4 device.

The optical performance of the three different display assemblies wasexamined using a commercial conoscope ELDIM L80 (ELDIM SA,Hérouville-Saint-Clair, France). The brightness and contrast results forthe display assemblies are shown in Table 7 with the values normalizedto with respect to the Comparative AP/RP film. As shown from theresults. The optical film of Example 1 showed superior brightnesscompared to both the Comparative AP/RP and RP films. Additionally, theoptical film of Example 1 exhibited a contrast ratio that was fargreater than that of the stock Comparative RP film alone and remainedcomparable to that of the Comparative AP/RP despite the absence of arear AP layer in the display assembly.

TABLE 7 Film Sample in Display Test Brightness* Contrast RatioComparative AP/RP film 100% 1000:1 Comparative RP film 102%  25:1Example 1 (HCRP) 112%  580:1 *Values are normalized with respect to theComparative AP/RP film

Clause 1: In one example, an optical film including a plurality ofinterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, a total number of theinterference layers less than about 1000, such that for a substantiallynormally incident light in a predetermined wavelength range, theplurality of interference layers has an average optical transmittancegreater than about 85% for a first polarization state, an averageoptical reflectance greater than about 80% for an orthogonal secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 2: In some examples of the optical film of clause 1, theplurality of interference layers has an average optical transmittancegreater than about 90% for the first polarization state in thepredetermined wavelength range.

Clause 3: In some examples of the optical film of clause 1, theplurality of interference layers has an average optical transmittancegreater than about 95% for the first polarization state in thepredetermined wavelength range.

Clause 4: In some examples of the optical film of clause 1, theplurality of interference layers has an average optical transmittancegreater than about 98% for the first polarization state in thepredetermined wavelength range.

Clause 5: In some examples of the optical film of any of the proceedingclauses, the plurality of interference layers has an average opticaltransmittance less than about 0.15% for the second polarization state inthe predetermined wavelength range.

Clause 6: In some examples of the optical film of any of the proceedingclauses, the plurality of interference layers has an average opticaltransmittance less than about 0.10% for the second polarization state inthe predetermined wavelength range.

Clause 7: In some examples of the optical film of any of the proceedingclauses, such that for light incident on the optical film at anincidence angle of about 10 degrees in the predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for the first polarization state,an average optical reflectance greater than about 80% for the secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 8: In some examples of the optical film of any of the proceedingclauses, such that for light incident on the optical film at anincidence angle of about 20 degrees in the predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for the first polarization state,an average optical reflectance greater than about 80% for the secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 9: In some examples of the optical film of clause 1, such thatfor light incident on the optical film at an incidence angle of about 30degrees in the predetermined wavelength range, the plurality ofinterference layers has an average optical transmittance greater thanabout 85% for the first polarization state, an average opticalreflectance greater than about 80% for the second polarization state,and an average optical transmittance less than about 0.2% for the secondpolarization state.

Clause 10: In one example, an optical film including a plurality ofinterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, a total number of theinterference layers less than about 1000, such that for a substantiallynormally incident light in a predetermined wavelength range, the opticalfilm has an average optical transmittance T_(a) and an average opticalreflectance R_(a) for a first polarization state, and an average opticaltransmittance T_(b) and an average optical reflectance R_(b) for anorthogonal second polarization state, T_(b)/R_(b) less than about 0.002and R_(a)/T_(a) less than about 0.17.

Clause 11: In some examples of the optical film of clause 10,T_(a)/T_(b) is greater than about 425.

Clause 12: In some examples of the optical film of clause 10 or 11,R_(b)/R_(a) is greater than about 6.7.

Clause 13: In some examples of the optical film of any of clauses 10 to12, the T_(a) for the plurality of interference layers is greater thanabout 90% in the predetermined wavelength range.

Clause 14: In some examples of the optical film of any of clauses 10 to13, the T_(a) for the plurality of interference layers is greater thanabout 95% in the predetermined wavelength range.

Clause 15: In some examples of the optical film of any of clauses 10 to14, the T_(a) for the plurality of interference layers is greater thanabout 98% in the predetermined wavelength range.

Clause 16: In some examples of the optical film of any of clauses 10 to15, the T_(b) is less than about 0.15% in the predetermined wavelengthrange.

Clause 17: In some examples of the optical film of any of clauses 10 to16, the T_(b) is less than about 0.10% in the predetermined wavelengthrange.

Clause 18: In some examples of the optical film of any of clauses 10 to17, such that for light incident on the optical film at an incidenceangle of about 10 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%.

Clause 19: In some examples of the optical film of any of clauses 10 to18, such that for light incident on the optical film at an incidenceangle of about 20 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%.

Clause 20: In some examples of the optical film of any of clauses 10 to19, such that for light incident on the optical film at an incidenceangle of about 30 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%

Clause 21: In some examples of the optical film of any of the precedingclauses, the optical film including at least one non-interference layerdisposed between two interference layers, each of the at least onenon-interference layer not reflecting or transmitting light primarily byoptical interference.

Clause 22: In some examples of the optical film of clause 21, an averagethickness of each of the at least one non-interference layer is at least10 times a largest wavelength in the predetermined wavelength range.

Clause 23: In some examples of the optical film of clause 21, an averagethickness of each of the at least one non-interference layer is at least50 times a largest wavelength in the predetermined wavelength range.

Clause 24: In some examples of the optical film of any of the precedingclauses, the predetermined wavelength range is from about 400 nm toabout 700 nm.

Clause 25: In some examples of the optical film of any of the precedingclauses, the predetermined wavelength range is from about 400 nm toabout 700 nm and from about 800 nm to about 1300 nm.

Clause 26: In some examples of the optical film of any of the precedingclauses, the total number of the interference layers is less than about900.

Clause 27: In some examples of the optical film of any of the precedingclauses, the total number of the interference layers is less than about800.

Clause 28: In some examples of the optical film of any of the precedingclauses, the optical film has a thickness of less than about 60 μm.

Clause 29: In some examples of the optical film of any of the precedingclauses, the plurality of interference layers includes pluralities ofalternating higher index first and lower index second layers.

Clause 30: In one example, an optical film including N sequentiallynumbered layers, N is an integer greater than 200 and less than 1000,each layer having an average thickness less than about 200 nm, a fittedcurve being a best-fit regression applied to a layer thickness profileplotting a thickness of each layer as a function of layer number, wherean average slope of the fitted curve in a region extending from thefirst layer to the Nth layer being less than about 0.2 nm/layer, suchthat for a substantially normally incident light in a predeterminedwavelength range, the optical film has an average optical transmittancegreater than about 85% for a first polarization state and an averageoptical reflectance greater than about 80% for an orthogonal secondpolarization state.

Clause 31: In one example, an optical film including N sequentiallynumbered layers, N is an integer greater than 200, with less than 10% ofthe layers having an average thickness more than about 200 nanometers(nm), a fitted curve being a best-fit regression applied to a layerthickness of the optical film as a function of layer number, an averageslope of the fitted curve in a region extending from the first layer tothe Nth layer being less than about 0.2 nm.

Clause 32: In some examples of the optical film of clause 31, where theaverage thickness of at least one numbered layer in the N sequentiallynumbered layers is at least 30% less than the average thickness of atleast one other numbered layer in the N sequentially numbered layers.

Clause 33: In some examples of the optical film of clause 30 or 32, thebest-fit regression is one or more of a best-fit linear regression, abest-fit non-linear regression, a best-fit polynomial regression, and abest-fit exponential regression.

Clause 34: In some examples of the optical film of any one of clauses 30to 33, the optical film including at least one spacer layer disposedbetween two sequentially numbered layers in the N sequentially numberedlayers, each spacer layer in the at least one spacer layer having anaverage thickness greater than about 500 nm.

Clause 35: In some examples of the optical film of any one of clauses 30to 34, the optical film including at least one spacer layer disposedbetween two sequentially numbered layers in the N sequentially numberedlayers, each spacer layer in the at least one spacer layer having anaverage thickness that is at least 10 times a largest wavelength in thepredetermined wavelength range.

Clause 36: In some examples of the optical film of any one of clauses 30to 35, the optical film including at least one spacer layer disposedbetween two sequentially numbered layers in the N sequentially numberedlayers, each spacer layer in the at least one spacer layer having anaverage thickness that is at least 50 times a largest wavelength in thepredetermined wavelength range.

Clause 37: In some examples of the optical film of any one of clauses 30to 36, the average thickness of at least one layer in the N sequentiallynumbered layers is less than about 50 nm, and the average thickness ofat least one other layer in the N sequentially numbered layers isgreater than about 100 nm.

Clause 38: In some examples of the optical film of any one of clauses 30to 37, the N sequentially numbered layers are sequentially arranged.

Clause 39: In some examples of the optical film of any one of clauses 30to 38, the best-fit regression is one or more of a best-fit linearregression, a best-fit non-linear regression, a best-fit polynomialregression, and a best-fit exponential regression.

Clause 40: In some examples of the optical film of any one of clauses 30to 39, the N sequentially numbered layers comprises pluralities ofalternating higher index first and lower index second layers.

Clause 41: In one example, an optical film including a plurality oflayers sequentially numbered from one to N, where N is an integergreater than 50 and less than 1000, the optical film transmitting atleast 80% of light having a first polarization state in a predeterminedwavelength range and reflecting at least 80% of light having anorthogonal second polarization state in the predetermined wavelengthrange, a fitted curve being a best-fit regression applied to a layerthickness of the optical film as a function of layer number, such thatin a region extending from the first layer to the Nth layer, adifference between a maximum slope and a minimum slope of the fittedcurve is less than about 0.70 nm/layer, where the maximum slope and theminimum slope are each evaluated over any group of 25 to 50 adjacentlayers.

Clause 42: In some examples of the optical film of clause 41, each layerin the plurality of layers has an average thickness less than about 200nm.

Clause 43: In some examples of the optical film of clause 41 or 42, thenumbered layers in the plurality of layers are sequentially arranged.

Clause 44: In some examples of the optical film of any of clauses 41 to43, an average slope of the fitted curve in a region extending from thefirst layer to the Nth layer being less than about 0.2 nm, such that fora substantially normally incident light in a predetermined wavelengthrange.

Clause 45: In some examples of the optical film of any of clauses 41 to44, the best-fit regression is one or more of a best-fit linearregression, a best-fit non-linear regression, a best-fit polynomialregression, and a best-fit exponential regression.

Clause 46: In some examples of the optical film of any of clauses 41 to45, the optical film including a spacer layer disposed between twosequentially numbered layers in the plurality of layers sequentiallynumbered from one to N, the spacer layer having an average thicknessthat is at least 10 times a largest wavelength in the predeterminedwavelength range.

Clause 47: In some examples of the optical film of clause 46, the spacerlayer having an average thickness that is at least 50 times a largestwavelength in the predetermined wavelength range.

Clause 48: In some examples of the optical film of any of clauses 41 to47, the average thickness of at least one layer in the plurality oflayers sequentially numbered from one to N is less than about 50 nm, andthe average thickness of at least one other layer in the plurality oflayers sequentially numbered from one to N is greater than about 100 nm.

Clause 49: In some examples of the optical film of any of clauses 41 to48, the N sequentially numbered layers includes pluralities ofalternating higher index first and lower index second layers.

Clause 50: In one example, an optical film transmitting at least 80% oflight having a first polarization state in a predetermined wavelengthrange and reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, the opticalfilm including a stack of N layers, where N is an integer greater than50 and less than 1000, such that, for a plurality of non-overlappinggroups of sequentially arranged layers in the stack of N layers, thelayers in each group numbered from one to m, m greater than 25, for eachnon-overlapping group a fitted curve is a best-fit regression applied toa layer thickness of the group as a function of layer number, where in aregion extending from the first layer in the group to the mth layer inthe group, the fitted curve has an average slope such that, a maximumdifference between the average slopes of the fitted curves in theplurality of non-overlapping groups is less than 0.70 nm/layer.

Clause 51: In some examples of the optical film of clause 51, theaverage thickness of at least one layer in the stack of N layers is atleast 30% less than the average thickness of at least one other layer inthe stack of N layers.

Clause 52: In some examples of the optical film of clause 51 or 52, thebest-fit regression is one or more of a best-fit linear regression, abest-fit non-linear regression, a best-fit polynomial regression, and abest-fit exponential regression.

Clause 53: In some examples of the optical film of any of clauses 50 to52, the average thickness of at least one layer in the stack of N layersis less than about 50 nm, and the average thickness of at least oneother layer in the stack of N layers is greater than about 100 nm.

Clause 54: In one example, an optical film including a plurality ofalternating first and second layers, each first layer and each secondlayer reflecting or transmitting light primarily by opticalinterference, a total number of each of the first and second layersbeing less than 400 and greater than 100, for each pair of adjacentfirst and second layers: in a plane of the first layer, the first layerhas a maximum index of refraction n1_(x) along an x-direction; thesecond layer has an index of refraction n2_(x) along the x-direction; adifference between n1_(x) and n2_(x) is greater than about 0.24; and amaximum angular range of the x-directions of the first layers is lessthan about 2 degrees.

Clause 55: In some examples of the optical film of clause 54, theplurality of alternating first and second layers are sequentiallyarranged.

Clause 56: In some examples of the optical film of clause 54 or 55, theplurality of alternating first and second layers includes a total of Nsequentially arranged layers, the optical film transmitting at least 80%of light having a first polarization state in a predetermined wavelengthrange and reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, a fitted curvebeing a best-fit regression applied to a layer thickness of the opticalfilm as a function of layer number, such that in a region extending froma first layer to a Nth layer includes a slope less than about 0.2nm/layer number.

Clause 57: In some examples of the optical film any of clauses 54 to 56,the best-fit regression is one or more of a best-fit linear regression,a best-fit non-linear regression, a best-fit polynomial regression, anda best-fit exponential regression.

Clause 58: In some examples of the optical film of any of clauses 54 to57, each layer in the plurality of alternating first and second layersan average thickness per layer of less than about 200 nm.

Clause 59: In some examples of the optical film of any of clauses 54 to58, the plurality of alternating first and second layers includes atleast two stacks each including at least some of the plurality ofalternating first and second layers, the optical film further includinga spacer layer disposed between the two stacks, the spacer layer havingan average thickness that is at least 10 times a largest wavelength inthe predetermined wavelength range.

Clause 60: In some examples of the optical film of clause 59, the spacerlayer having an average thickness that is at least 50 times a largestwavelength in the predetermined wavelength range.

Clause 61: In some examples of the optical film of any of clauses 54 to60, the average thickness of at least one layer in the plurality ofalternating first and second layers is less than about 50 nm, and theaverage thickness of at least one other layer in the plurality ofalternating first and second layers is greater than about 100 nm.

Clause 62: In one example, an optical film including a plurality ofalternating higher index of refraction and lower index of refractioninterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, a total number of theinterference layers greater than 300, an optical power of the opticalfilm per interference layer greater than about 0.7.

Clause 63: In some examples of the optical film of clause 62, the totalnumber of the higher index and lower index interferences layers is lessthan 1000.

Clause 64: In some examples of the optical film of clause 62 or 63, thehigher index and lower index interference layers includes at least twostacks each including at least some of the higher index and lower indexinterference layers, the optical film further including a spacer layerdisposed between the two stacks, the spacer layer having an averagethickness that is at least 10 times a largest wavelength in apredetermined wavelength range.

Clause 65: In some examples of the optical film of any of clauses 62 to64, the spacer layer having an average thickness that is at least 50times a largest wavelength in the predetermined wavelength range.

Clause 66: In some examples of the optical film of any of clauses 62 to65, the average thickness of at least one layer in the plurality ofalternating higher index and lower index interference layers is lessthan about 50 nm, and the average thickness of at least one other layerin the plurality of alternating higher index and lower indexinterference layers is greater than about 100 nm.

Clause 67: In one example, an optical film including a plurality ofalternating higher index of refraction and lower index of refractioninterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, an optical power of theplurality of the interference layers per interference layer beinggreater than −0.0012*N+1.46, where N is a total number of thealternating higher index and lower index interference layers, N beinggreater than 100 and less than 1000.

Clause 68: In some examples of the optical film of clause 67, the totalnumber of the higher index and lower index interferences layers is lessthan 1000.

Clause 69: In some examples of the optical film of clause 67 or 68, thehigher index and lower index interference layers includes at least twostacks each including at least some of the higher index and lower indexinterference layers, the optical film further including a spacer layerdisposed between the two stacks, the spacer layer having an averagethickness that is at least 10 times a largest wavelength in apredetermined wavelength range.

Clause 70: In some examples of the optical film of clause 69, the spacerlayer having an average thickness that is at least 50 times a largestwavelength in the predetermined wavelength range.

Clause 71: In some examples of the optical film of any of clauses 67 to70, the average thickness of at least one layer in the plurality ofalternating higher index and lower index interference layers is lessthan about 50 nm, and the average thickness of at least one other layerin the plurality of alternating higher index and lower indexinterference layers is greater than about 100 nm.

Clause 72: In one example, an optical film including a plurality ofinterference layers reflecting and transmitting light primarily byoptical interference, such that for a substantially normally incidentlight in a predetermined wavelength range, the plurality of theinterference layers transmit at least 80% of light having a firstpolarization state, reflect at least 80% of light having an orthogonalsecond polarization state, and have an average optical density greaterthan about 2.5, the plurality of the interference layers divided into aplurality of optical stacks, each pair of adjacent optical stacksseparated by one or more spacer layers not reflecting or transmittinglight primarily by optical interference, each optical stack transmittingat least 50% of light having the first polarization state in thepredetermined wavelength range and reflecting at least 50% of lighthaving the second polarization state in the predetermined wavelengthrange, the interference layers in each optical stack sequentiallynumbered, each optical stack having a best-fit linear equationcorrelating a thickness of the optical stack to interference layernumber, the linear equation having an average slope in a regionextending from the first interference layer in the stack to the lastinterference layer in the stack, a maximum difference between theaverage slopes of the linear equations of the plurality of opticalstacks being less than about 20%.

Clause 73: In some examples of the optical film of clause 72, eachoptical stack includes at least 50 interference layers of the pluralityof the interference layers.

Clause 74: In some examples of the optical film of clause 72 or 73, theoptical film includes less than 1000 layers of the plurality ofinterference layers.

Clause 75: In some examples of the optical film of any of clauses 72 to74, the one or more spacer layers having an average thickness that is atleast 10 times a largest wavelength in a predetermined wavelength range.

Clause 76: In some examples of the optical film of any of clauses 72 to75, the one or more spacer layers having an average thickness that is atleast 50 times a largest wavelength in the predetermined wavelengthrange.

Clause 77: In some examples of the optical film of any of clauses 72 to76, the average thickness of at least one layer in the plurality ofinterference layers is less than about 50 nm, and the average thicknessof at least one other layer in the plurality of interference layers isgreater than about 100 nm.

Clause 78: In one example, an optical film transmitting at least 80% oflight having a first polarization state in a predetermined wavelengthrange and reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, the opticalfilm including: no less than 100 and no greater than 400 sequentiallyarranged unit cells, each unit cell including a lower index orrefraction first layer and an adjacent higher index of refraction secondlayer, a difference between the higher and lower indices of refractionfor each unit cell greater than about 0.24, each unit cell having atotal optical thickness equal to one half of a different centralwavelength in a predetermined wavelength range, such that for each of atleast 80% of pairs of adjacent unit cells in the sequentially arrangedunit cells, a ratio of a difference of the central wavelengths ofadjacent unit cells to an average of the central wavelengths of theadjacent unit cells is less than about 2%.

Clause 79: In some examples of the optical film of clause 78, theaverage thickness of at least one layer in the sequentially arrangedunit cells is at least 30% less than the average thickness of at leastone other layer in the sequentially arranged unit cells.

Clause 80: In some examples of the optical film of clause 78 or 79, thesequentially arranged unit cells includes a total of N sequentiallyarranged layers, each layer of the N sequentially arranged layers havingan average thickness less than about 200 nm, a fitted curve being abest-fit regression applied to a layer thickness of the optical film asa function of layer number, an average slope of the fitted curve in aregion extending from the first layer to the Nth layer being less thanabout 0.2 nm, such that for a substantially normally incident light in apredetermined wavelength range, the optical film has an average opticaltransmittance greater than about 80% for a first polarization state andan average optical reflectance greater than about 80% for an orthogonalsecond polarization state.

Clause 81: In some examples of the optical film of any of clauses 78 to80, the best-fit regression is one or more of a best-fit linearregression, a best-fit non-linear regression, a best-fit polynomialregression, and a best-fit exponential regression.

Clause 82: In some examples of the optical film of any of clauses 78 to81, the average thickness of at least one layer in the stack of Nsequentially arranged layers is less than about 50 nm, and the averagethickness of at least one other layer in the stack of N sequentiallyarranged layers is greater than about 100 nm.

Clause 83: In one example, an optical film including a plurality ofinterference layers reflecting or transmitting light primarily byoptical interference in a predetermined wavelength range, a maximumdifference between indices of refraction of the interference layersbeing Δn, a fitted curve being a best-fit regression applied to a layerthickness of the optical film as a function of layer number, the fittedcurve having an average slope K in a region extending across theplurality of interference layers, Δn/K greater than about 1.2.

Clause 84: In some examples of the optical film of clause 83, Δn/Kgreater than about 1.5.

Clause 85: In some examples of the optical film of clause 83 or 84,having an optical density of greater than about 2.0 in the predeterminedwavelength range.

Clause 86: In some examples of the optical film of any of clauses 83 to85, having an optical density of greater than about 3.0 in thepredetermined wavelength range.

Clause 87: In some examples of the optical film of any of clauses 83 to86, having an optical density of greater than about 3.0 in thepredetermined wavelength range.

Clause 88: In some examples of the optical film of any of clauses 83 to87, Δn is greater than about 0.24.

Clause 89: In some examples of the optical film of any of clauses 83 to88, the plurality of interference layers includes a total of Nsequentially arranged layers, N being less than 1000, each layer of theN sequentially arranged layers having an average thickness less thanabout 200 nm, a fitted curve being a best-fit regression applied to alayer thickness of the optical film as a function of layer number, anaverage slope of the fitted curve in a region extending from the firstlayer to the Nth layer being less than about 0.2 nm, such that for asubstantially normally incident light in a predetermined wavelengthrange, the optical film has an average optical transmittance greaterthan about 80% for a first polarization state and an average opticalreflectance greater than about 80% for an orthogonal second polarizationstate.

Clause 90: In some examples of the optical film of clause 89, thebest-fit regression is one or more of a best-fit linear regression, abest-fit non-linear regression, a best-fit polynomial regression, and abest-fit exponential regression.

Clause 91: In some examples of the optical film of clause 89 or 90,where the average thickness of at least one layer in the N sequentiallyarranged layers is less than about 50 nm, and the average thickness ofat least one other layer in the N sequentially arranged layers isgreater than about 100 nm.

Clause 92: In some examples of the optical film of any of clauses 83 to91, the optical film including a spacer layer disposed between twolayers of the plurality of interference layers, the spacer layer havingan average thickness that is at least 10 times a largest wavelength inthe predetermined wavelength range.

Clause 93: In some examples of the optical film of clause 92, the spacerlayer having an average thickness that is at least 50 times a largestwavelength in the predetermined wavelength range.

Clause 94: In one example, an optical film including M_(a) sequentiallyarranged first unit cells optimized to transmit or reflect light in afirst, but not second, predetermined wavelength range, each of the firstunit cells including a first high index of refraction layer and a secondlow index of refraction layer; and M_(b) sequentially arranged secondunit cells optimized to transmit or reflect light in the second, but notthe first, predetermined wavelength range, each of the second unit cellsincluding a third high index of refraction layer and a fourth low indexof refraction layer, such that: for the M_(a) sequentially arrangedfirst unit cells, a ratio of an average of indices of refraction of thefirst high index of refraction layers to an average of indices ofrefraction of the second low index of refraction layers times M_(a) isgreater than about 300; and

for the M_(b) sequentially arranged second unit cells show, a ratio ofan average of indices of refraction of the third high index ofrefraction layers to an average of indices of refraction of the fourthlow index of refraction layer times M_(b) is greater than about 300,where for light incident on the optical film at any incidence angle fromabout zero degree to about 30 degrees having any wavelength in the firstand second predetermined wavelength ranges, a ratio of an averageoptical transmittance T_(a) of the optical film for a first polarizationstate to an average optical transmittance T_(b) of the optical film foran orthogonal second polarization state is no less than about 1000:1.

Clause 95: In some examples of the optical film of clause 94, the firstand second predetermined wavelength ranges are in respective visible andinfrared ranges of an electromagnetic spectrum.

Clause 96: In some examples of the optical film of clause 94 or 95, thefirst predetermined wavelength range is from about 400 nm to about 700nm.

Clause 97: In some examples of the optical film of any of clauses 94 to96, the second predetermined wavelength range is from about 800 nm toabout 1300 nm.

Clause 98: In some examples of the optical film of any of clauses 94 to97, the M_(a) sequentially arranged first unit cells and M_(b)sequentially arranged second unit cells each includes less than about400 total interference layers, each interference layer having an averagethickness less than about 200 nm, a fitted curve being a best-fitregression applied to a layer thickness of the M_(a) sequentiallyarranged first unit cells as a function of layer number, an averageslope of the fitted curve in a region extending from the firstinterference layer to the (2*Ma) layer being less than about 0.2nm/layer number, such that for a substantially normally incident lightin the first predetermined wavelength range, the optical film has anaverage optical transmittance greater than about 80% for the firstpolarization state and an average optical reflectance greater than about80% for the orthogonal second polarization state.

Clause 99: In some examples of the optical film of any of clauses 94 to98, the best-fit regression is one or more of a best-fit linearregression, a best-fit non-linear regression, a best-fit polynomialregression, and a best-fit exponential regression.

Clause 100: In some examples of the optical film of any of clauses 94 to99, where the average thickness of at least one interference layer inthe M_(a) sequentially arranged first unit cells is less than about 50nm, and the average thickness of at least one other interference layerin the M_(a) sequentially arranged first unit cells is greater thanabout 100 nm.

Clause 101: In some examples of the optical film of any of clauses 94 to100, the optical film including a spacer layer disposed between theM_(a) sequentially arranged first unit cells and the M_(b) sequentiallyarranged second unit cells, the spacer layer having an average thicknessthat is at least 10 times a largest wavelength in the first and secondpredetermined wavelength ranges.

Clause 102: In some examples of the optical film of clause 101, thespacer layer having an average thickness that is at least 50 times alargest wavelength in the first and second predetermined wavelengthranges.

Clause 103: In some examples of the optical film of any of clauses 30 to100, where, for a substantially normally incident light in apredetermined wavelength range, the optical film has an average opticaltransmittance T_(a) and an average optical reflectance R_(a) for a firstpolarization state, and an average optical transmittance T_(b) and anaverage optical reflectance R_(b) for an orthogonal second polarizationstate, T_(b)/R_(b) less than about 0.002 and R_(a)/T_(a) less than about0.17.

Clause 104: In some examples of the optical film of clause 103,T_(a)/T_(b) is greater than about 425.

Clause 105: In some examples of the optical film of clause 103 or 104,R_(b)/R_(a) is greater than about 6.7.

Clause 106: In some examples of the optical film of any of clauses 103to 105, the predetermined wavelength range is from about 400 nm to about700 nm.

Clause 107: In some examples of the optical film of any of clauses 103to 106, the predetermined wavelength range is from about 400 nm to about700 nm and from about 800 nm to about 1300 nm.

Clause 108: In some examples of the optical film of any of clauses 103to 107, the T_(a) for the layers is greater than about 90% in thepredetermined wavelength range.

Clause 109: In some examples of the optical film of any of clauses 103to 108, the T_(a) for the layers is greater than about 95% in thepredetermined wavelength range.

Clause 110: In some examples of the optical film of any of clauses 103to 109, the T_(a) for the layers is greater than about 98% in thepredetermined wavelength range.

Clause 111: In some examples of the optical film of any of clauses 103to 110, the T_(b) is less than about 0.15% in the predeterminedwavelength range.

Clause 112: In some examples of the optical film of any of clauses 103to 111, the T_(b) is less than about 0.10% in the predeterminedwavelength range.

Clause 113: In some examples of the optical film of any of clauses 103to 112, such that for light incident on the optical film at an incidenceangle of about 10 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%.

Clause 114: In some examples of the optical film of any of clauses 103to 113, such that for light incident on the optical film at an incidenceangle of about 20 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%.

Clause 115: In some examples of the optical film of any of clauses 103to 114, such that for light incident on the optical film at an incidenceangle of about 30 degrees in the predetermined wavelength range, theT_(a) is greater than about 85%, the R_(b) is greater than about 80%,and T_(b) is less than about 0.2%.

Clause 116: In some examples of the optical film of any of clauses 30 to115, the optical film has a thickness of less than about 60 μm.

Clause 117: In some examples of the optical film of any of clauses 30 to116, the layers include pluralities of alternating higher index firstand lower index second layers.

Clause 118: In some examples of the optical film of any of clauses 30 to117, the total number of the layers is less than about 900.

Clause 119: In some examples of the optical film of any of clauses 30 to118, the total number of the layers is less than about 800.

Clause 120: In some examples of the optical film of any of theproceeding clauses, the optical film has a contrast ratio of greaterthan 1000:1.

Clause 121: In some examples of the optical film of any of theproceeding clauses, the optical film has an optical density of greaterthan about 2.0 in the predetermined wavelength range.

Clause 122: In some examples of the optical film of any of theproceeding clauses, the optical film has an optical power perinterference layer greater than about 0.7.

Clause 123: In some examples of the optical film of any of theproceeding clauses, the predetermined wavelength range includes threepredetermined wavelength ranges from about 430 nm to about 465 nm, 490nm to about 555 nm, and about 600 nm to about 665 nm.

Clause 124: In some examples of the optical film of any of theproceeding clauses, where the alternating higher index first and lowerindex second layers define a difference between indices of refractiongreater than about 0.24 for an axis corresponding to the firstpolarization state.

Clause 125: In some examples of the optical film of clause 124, where amaximum difference between indices of refraction of the alternatinghigher index first and lower index second layers being Δn, a fittedcurve being a best-fit regression applied to a layer thickness of theoptical film as a function of layer number, the fitted curve having anaverage slope K in a region extending across the plurality ofinterference layers, Δn/K greater than about 1.2.

Clause 126: In some examples of the optical film of clause 125, whereΔn/K greater than about 1.5.

Clause 127: In one example, a display assembly including a light source;a liquid crystal display assembly; and the optical film of any of theproceeding clauses disposed between the liquid crystal display assemblyand the light source.

Clause 128: In some examples of the display assembly of clause 127, thelight source includes a light guide configured to direct light towardsthe optical film, where the liquid crystal display assembly includes: aliquid crystal layer; and an absorption polarizer, where the liquidcrystal layer is disposed between the optical film and the absorptionpolarizer.

Clause 129: In some examples of the display assembly of clause 127 or128, the display assembly does not include an absorption polarizer filmbetween the liquid crystal layer and the optical film.

Clause 130: In some examples of the display assembly of clause 127 or128, the display assembly further includes an absorption polarizerdisposed between the liquid crystal layer and the optical film.

Clause 131: In one example, a display assembly including: a lightsource; a liquid crystal layer configured to be illuminated by the lightsource; one or more brightness enhancement films disposed between thelight source and the liquid crystal layer for increasing an axialbrightness of the display assembly; and a reflective polarizer disposedbetween the one or more brightness enhancement films and the liquidcrystal layer and configured to substantially transmit light having afirst polarization state and substantially reflect light having anorthogonal second polarization state, the reflective polarizer having anaverage optical transmittance less than about 0.2% for the secondpolarization state, where no absorbing polarizer is disposed between thelight source and the liquid crystal layer, and where a contrast ratio ofthe display assembly is at least twice that of a comparative displayassembly having the same construction except that the averagetransmittance of the reflective polarizer of the comparative displayassembly for the second polarization state is greater than about 1.0%.

Clause 132: In some examples of the display assembly of clause 131, thereflective polarizer includes the optical film of any one of clauses 1to 126.

Clause 133: In one example, a display assembly including a light source;a liquid crystal layer configured to be illuminated by the light source;one or more brightness enhancement films disposed between the lightsource and the liquid crystal layer for increasing an axial brightnessof the display assembly; and a reflective polarizer disposed between theone or more brightness enhancement films and the liquid crystal layerand including a plurality of interference layers transmitting orreflecting light primarily by optical interference, such that for asubstantially normally incident light in a predetermined wavelengthrange, the plurality of the interference layers transmits at least 80%of light having a first polarization state and transmits less than about0.2% of light having an orthogonal second polarization state, where noabsorbing polarizer is disposed between the light source and the liquidcrystal layer.

Clause 134: In some examples of the display assembly of clause 133, thereflective polarizer includes the optical film of any one of clauses 1to 126.

Clause 135: In one example, an optical stack including a reflectivepolarizer including a plurality of interference layers, eachinterference layer reflecting or transmitting light primarily by opticalinterference, for a substantially normally incident light having apredetermined wavelength, the plurality of interference layers having anoptical transmittance greater than about 85% for a first polarizationstate, an optical reflectance greater than about 80% for an orthogonalsecond polarization state, and an optical transmittance less than about0.1% for the second polarization state; and an absorbing polarizerbonded to and substantially co-extensive with the reflective polarizer,for a substantially normally incident light having the predeterminedwavelength, the absorbing polarizer having a first optical transmittancefor the first polarization state, an optical absorption greater thanabout 50% for the second polarization state, and a second opticaltransmittance for the second polarization state, a ratio of the secondoptical transmittance to the first optical transmittance being greaterthan about 0.001.

Clause 136: In some examples of the optical stack of clause 135, theratio of the second optical transmittance to the first opticaltransmittance is greater than about 0.01.

Clause 137: In some examples of the optical stack of clause 135 or 136,the ratio of the second optical transmittance to the first opticaltransmittance is greater than about 0.1.

Clause 138: In some examples of the optical stack of any one of clauses135 to 137, the predetermined wavelength is about 550 nm.

Clause 139: In some examples of the optical stack of any one of clauses135 to 138, the reflective polarizer includes the optical film of anyone of clauses 1 to 126.

Clause 140: In one example, an optical system for displaying an objectto a viewer centered on an optical axis and including: at least oneoptical lens having a non-zero optical power; a reflective polarizerdisposed on and conforming to a first major surface of the optical lens,the reflective polarizer substantially transmitting light having a firstpolarization state and substantially reflecting light having anorthogonal second polarization state; and a partial reflector disposedon and conforming to a different second major surface of the opticallens, the partial reflector having an average optical reflectance of atleast 30% for a predetermined wavelength range, such that an averageoptical transmittance of the optical system for an incident light alongthe optical axis having the second polarization state is less than about0.1%.

Clause 141: In some examples of the optical system of clause 140, thereflective polarizer includes N sequentially numbered interferencelayers, where N is an integer greater than 50, each layer having anaverage thickness less than about 200 nm, a fitted curve being abest-fit regression applied to a layer thickness profile plotting athickness of each layer as a function of layer number, where an averageslope of the fitted curve in a region extending from the first layer tothe Nth layer being less than about 0.2 nm/layer.

Clause 142: In some examples of the optical system of clause 140 or 141,the reflective polarizer includes the optical film of any one of clauses1 to 126.

Clause 143: In some examples of the optical system of any of clauses 140to 142, the first major surface of the at least one optical lens iscurved along at least a first direction.

Clause 144: In some examples of the optical system of any of clauses 140to 143, the second major surface of the at least one optical lens iscurved along at least a first direction.

Clause 145: In some examples of the optical system of any of clauses 140to 144, each of the first and second major surfaces is curved along twomutually orthogonal directions.

Clause 146: In one example, a polarizing beam splitter (PBS) including:a first and second prism; and a reflective polarizer disposed betweenand adhered to the first and second prisms, the reflective polarizersubstantially reflecting polarized light having a first polarizationstate and substantially transmitting polarized light having anorthogonal second polarization state, such that when an incident lighthaving a predetermined wavelength enters the PBS from an input side ofthe PBS and exits the PBS from an output side of the PBS afterencountering the reflective polarizer at least once, a ratio of anaverage intensity of the exiting light to an average intensity of theincident light is: greater than about 90% when the incident light hasthe first polarization state, and less than about 0.2% when the incidentlight has the second polarization state.

Clause 147: In some examples of the PBS of clause 146, the reflectivepolarizer includes N sequentially numbered interference layers, where Nis an integer greater than 50, each layer having an average thicknessless than about 200 nm, a fitted curve being a best-fit regressionapplied to a layer thickness profile plotting a thickness of each layeras a function of layer number, where an average slope of the fittedcurve in a region extending from the first layer to the Nth layer beingless than about 0.2 nm/layer.

Clause 148: In some examples of the PBS of clause 146 or 147, thereflective polarizer includes the optical film of any one of clauses 1to 126.

Clause 149: In some examples of the PBS of any one of clauses 146 to148, at least one of the first and second prisms is polymeric.

Clause 150: In some examples of the PBS of any one of clauses 146 to149, the pre-determined wavelength is in a range from about 400 nm toabout 700 nm.

Clause 151: In one example, a liquid crystal display projection systemincluding the optical film of any one of clauses 1 to 126.

Clause 152: In some examples of the liquid crystal display projectionsystem of clause 151, the system including one or more light waveretarder layers positioned next to the optical film, the one or morelight wave retarder layers configured to modify a polarization state ofincident light.

Clause 153: In some examples of the liquid crystal display projectionsystem of clause 152, at least one of the light wave retarder layers isoptically coupled directly to the optical film.

Clause 154: In some examples of the liquid crystal display projectionsystem of clause 152 or 153, at least one of the light wave retarderlayers is spaced apart from the optical film.

Clause 155: In one example, a display assembly including: a lightsource; a liquid crystal layer configured to be illuminated by the lightsource; and a reflective polarizer including the optical film of any oneof clauses 1 to 126, the reflective polarizer disposed adjacent to theliquid crystal layer.

Clause 156: In one example, an optical film comprising a plurality ofinterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, a total number of theinterference layers less than about 800, such that for a substantiallynormally incident light in a predetermined wavelength range, theplurality of interference layers has an average optical transmittancegreater than about 85% for a first polarization state, an averageoptical reflectance greater than about 80% for an orthogonal secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 157: In some examples of the optical film of clause 156, theoptical film further comprising at least one noninterference layerdisposed between two interference layers, each of the at least onenoninterference layer not reflecting or transmitting light primarily byoptical interference.

Clause 158: In some examples of the optical film of clause 157, anaverage thickness of each of the at least one noninterference layer isat least 10 times a largest wavelength in the predetermined wavelengthrange.

Clause 159: In some examples of the optical film of clause 157, anaverage thickness of each of the at least one noninterference layer isat least 50 times a largest wavelength in the predetermined wavelengthrange.

Clause 160: In some examples of the optical film of clause 156, thepredetermined wavelength range is from about 400 nm to about 700 nm.

Clause 161: In some examples of the optical film of clause 156, thepredetermined wavelength range is from about 400 nm to about 700 nm andfrom about 800 nm to about 1300 nm.

Clause 162: In some examples of the optical film of clause 156, theplurality of interference layers comprises pluralities of alternatinghigher index first and lower index second layers.

Clause 163: In some examples of the optical film of clause 156, theplurality of interference layers has an average optical transmittancegreater than about 90% for the first polarization state in thepredetermined wavelength range.

Clause 164: In some examples of the optical film of clause 156, theplurality of interference layers has an average optical transmittancegreater than about 95% for the first polarization state in thepredetermined wavelength range.

Clause 165: In some examples of the optical film of clause 156, theplurality of interference layers has an average optical transmittancegreater than about 98% for the first polarization state in thepredetermined wavelength range.

Clause 166: In some examples of the optical film of clause 156, theplurality of interference layers has an average optical transmittanceless than about 0.15% for the second polarization state in thepredetermined wavelength range.

Clause 167: In some examples of the optical film of clause 156, theplurality of interference layers has an average optical transmittanceless than about 0.10% for the second polarization state in thepredetermined wavelength range.

Clause 168: In some examples of the optical film of clause 156, theoptical film such that for light incident on the optical film at anincidence angle of about 10 degrees in the predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for the first polarization state,an average optical reflectance greater than about 80% for the secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 169: In some examples of the optical film of clause 156, theoptical film such that for light incident on the optical film at anincidence angle of about 20 degrees in the predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for the first polarization state,an average optical reflectance greater than about 80% for the secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 170: In some examples of the optical film of clause 156, theoptical film such that for light incident on the optical film at anincidence angle of about 30 degrees in the predetermined wavelengthrange, the plurality of interference layers has an average opticaltransmittance greater than about 85% for the first polarization state,an average optical reflectance greater than about 80% for the secondpolarization state, and an average optical transmittance less than about0.2% for the second polarization state.

Clause 171: In one example, an optical film comprising a plurality ofinterference layers, each interference layer reflecting or transmittinglight primarily by optical interference, a total number of theinterference layers less than about 800, such that for a substantiallynormally incident light in a predetermined wavelength range, the opticalfilm has an average optical transmittance T_(a) and an average opticalreflectance R_(a) for a first polarization state, and an average opticaltransmittance T_(b) and an average optical reflectance R_(b) for anorthogonal second polarization state, T_(b)/R_(b) less than about 0.002and R_(a)/T_(a) less than about 0.17.

Clause 172: In some examples of the optical film of clause 171, theplurality of interference layers are sequentially arranged.

Clause 173: In some examples of the optical film of clause 171, theoptical film further comprising at least one noninterference layerdisposed between two interference layers in the plurality ofinterference layers, each of the at least one noninterference layer notreflecting or transmitting light primarily by optical interference.

Clause 174: In some examples of the optical film of clause 171,T_(a)/T_(b) is greater than about 425.

Clause 175: In some examples of the optical film of clause 171,R_(b)/R_(a) is greater than about 6.7.

Clause 176: In one example, an optical film comprising N sequentiallynumbered layers, N an integer greater than 200 and less than 800, eachlayer having an average thickness less than about 200 nm, a fitted curvebeing a best-fit regression applied to a thickness of the optical filmas a function of layer number, an average slope of the fitted curve in aregion extending from the first layer to the Nth layer being less thanabout 0.2 nm, such that for a substantially normally incident light in apredetermined wavelength range, the optical film has an average opticaltransmittance greater than about 85% for a first polarization state andan average optical reflectance greater than about 80% for an orthogonalsecond polarization state.

Clause 177: In some examples of the optical film of clause 176, the Nsequentially numbered layers are sequentially arranged.

Clause 178: In some examples of the optical film of clause 176, thebest-fit regression is one or more of a best-fit linear regression, abest-fit non-linear regression, a best-fit polynomial regression, and abest-fit exponential regression.

Clause 179: In some examples of the optical film of clause 176, theoptical film further comprising a spacer layer disposed between twosequentially numbered layers in the N sequentially numbered layers, thespacer layer having an average thickness that is at least 10 times alargest wavelength in the predetermined wavelength range.

Clause 180: In some examples of the optical film of clause 176, theaverage thickness of at least one layer in the N sequentially numberedlayers is less than about 50 nm, and the average thickness of at leastone other layer in the N sequentially numbered layers is greater thanabout 100 nm.

Clause 181: In one example, an optical film comprising N sequentiallynumbered layers, N an integer greater than 200, each layer having anaverage thickness less than about 200 nm, a fitted curve being abest-fit regression applied to a thickness of the optical film as afunction of layer number, an average slope of the fitted curve in aregion extending from the first layer to the Nth layer being less thanabout 0.2 nm.

Clause 182: In some examples of the optical film of clause 181, theoptical film further comprising at least one spacer layer disposedbetween two sequentially numbered layers in the N sequentially numberedlayers, each spacer layer in the at least one spacer layer having anaverage thickness greater than about 500 nm.

Clause 183: In some examples of the optical film of clause 181, the Nsequentially numbered layers are sequentially arranged.

Clause 184: In some examples of the optical film of clause 181, theaverage thickness of at least one numbered layer in the N sequentiallynumbered layers is at least 30% less than the average thickness of atleast one other numbered layer in the N sequentially numbered layers.

Clause 185: In one example, an optical film comprising a plurality oflayers sequentially numbered from one to N, N an integer greater than 50and less than 800, the optical film transmitting at least 80% of lighthaving a first polarization state in a predetermined wavelength rangeand reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, a fitted curvebeing a best-fit regression applied to a thickness of the optical filmas a function of layer number, such that in a region extending from thefirst layer to the Nth layer, a difference between a maximum slope and aminimum slope of the fitted curve is less than about 0.70 nm/layer.

Clause 186: In some examples of the optical film of clause 185, eachlayer in the plurality of layers has an average thickness less thanabout 200 nm.

Clause 187: In some examples of the optical film of clause 181, thenumbered layers in the plurality of layers are sequentially arranged.

Clause 188: In one example, an optical film transmitting at least 80% oflight having a first polarization state in a predetermined wavelengthrange and reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, the opticalfilm comprising a stack of N layers, N an integer greater than 50 andless than 800, such that, for a plurality of non-overlapping groups ofsequentially arranged layers in the stack of N layers, the layers ineach group numbered from one to m, m greater than N/10, for each group:a fitted curve is a best-fit regression applied to a thickness of thegroup as a function of layer number; and in a region extending from thefirst layer in the group to the mth layer in the group, the fitted curvehas an average slope, such that, a maximum difference between theaverage slopes of the fitted curves in the plurality of non-overlappinggroups is less than 0.70 nm/layer.

Clause 189: In one example, an optical film comprising a plurality ofalternating first and second layers, each first layer and each secondlayer reflecting or transmitting light primarily by opticalinterference, a total number of each of the first and second layersbeing less than 400 and greater than 100, for each pair of adjacentfirst and second layers: in a plane of the first layer, the first layerhas a maximum index of refraction n 1 along an x-direction; the secondlayer has an index of refraction n2, along the x-direction; a differencebetween n1_(x) and n2_(x) is greater than about 0.24; and a maximumangular range of the x-directions of the first layers is less than about2 degrees.

Clause 190: In some examples of the optical film of clause 189, theplurality of alternating first and second layers are sequentiallyarranged.

Clause 191: In one example, an optical film comprising a plurality ofalternating higher index and lower index interference layers, eachinterference layer reflecting or transmitting light primarily by opticalinterference, a total number of the layers greater than 300, an opticalpower of the optical film per interference layer greater than about 0.7.

Clause 192: In some examples of the optical film of clause 191, thetotal number of the interferences layers is less than 800.

Clause 193: In one example, an optical film comprising a plurality ofalternating higher index and lower index interference layers, eachinterference layer reflecting or transmitting light primarily by opticalinterference, an optical power of the plurality of the interferencelayers per interference layer being greater than −0.0012*N+1.5, where Nis a total number of the interference layers, N being greater than 100and less than 1000.

Clause 194: In one example, an optical film comprising a plurality ofinterference layers reflecting and transmitting light primarily byoptical interference, such that for a substantially normally incidentlight in a predetermined wavelength range, the plurality of theinterference layers transmit at least 80% of light having a firstpolarization state, reflect at least 80% of light having an orthogonalsecond polarization state, and have an average optical density greaterthan about 2.5, the plurality of the interference layers divided into aplurality of optical stacks, each pair of adjacent optical stacksseparated by one or more spacer layers not reflecting or transmittinglight primarily by optical interference, each optical stack transmittingat least 50% of light having the first polarization state in thepredetermined wavelength range and reflecting at least 50% of lighthaving the second polarization state in the predetermined wavelengthrange, the interference layers in each optical stack sequentiallynumbered, each optical stack having a best-fit linear equationcorrelating a thickness of the optical stack to interference layernumber, the linear equation having an average slope in a regionextending from the first interference layer in the stack to the lastinterference layer in the stack, a maximum difference between theaverage slopes of the linear equations of the plurality of opticalstacks being less than about 20%.

Clause 195: In some examples of the optical film of clause 194, eachoptical stack includes at least 50 interference layers of the pluralityof the interference layers.

Clause 196: In one example, a display system comprising: a light source;a liquid crystal layer configured to be illuminated by the light source;one or more brightness enhancement films disposed between the lightsource and the liquid crystal layer for increasing an axial brightnessof the display system; and a reflective polarizer disposed between theone or more brightness enhancement films and the liquid crystal layerand configured to substantially transmit light having a firstpolarization state and substantially reflect light having an orthogonalsecond polarization stated, the reflective polarizer having an averageoptical transmittance less than about 0.2% for the second polarizationstate, wherein no absorbing polarizer is disposed between the lightsource and the liquid crystal layer, and wherein a contrast ratio of thedisplay system is at least twice that of a comparative display systemhaving the same construction except that the average transmittance ofthe reflective polarizer of the comparative display system for thesecond polarization state is greater than about 1.0%.

Clause 197: In one example, a display system comprising: a light source;a liquid crystal layer configured to be illuminated by the light source;one or more brightness enhancement films disposed between the lightsource and the liquid crystal layer for increasing an axial brightnessof the display system; and a reflective polarizer disposed between theone or more brightness enhancement films and the liquid crystal layerand comprising a plurality of interference layers transmitting orreflecting light primarily by optical interference, such that for asubstantially normally incident light in a predetermined wavelengthrange, the plurality of the interference layers transmits at least 80%of light having a first polarization state and transmits less than about0.2% of light having an orthogonal second polarization state, wherein noabsorbing polarizer is disposed between the light source and the liquidcrystal layer.

Clause 198: In one example, an optical film transmitting at least 80% oflight having a first polarization state in a predetermined wavelengthrange and reflecting at least 80% of light having an orthogonal secondpolarization state in the predetermined wavelength range, the opticalfilm comprising no less than 200 and no greater than 400 sequentiallyarranged unit cells, each unit cell comprising a lower index first layerand an adjacent higher index second layer, a difference between thehigher and lower indices for each unit cell greater than about 0.24,each unit cell having a total optical thickness equal to one half of adifferent central wavelength in the predetermined wavelength range, suchthat for each of at least 80% of pairs of adjacent unit cells in thesequentially arranged unit cells, a ratio of a difference of the centralwavelengths of the unit cells to an average of the central wavelengthsof the unit cells is less than about 2%.

Clause 199: In one example, an optical film comprising a plurality ofinterference layers reflecting or transmitting light primarily byoptical interference in a predetermined wavelength range, a maximumdifference between indices of refraction of the interference layersbeing Δn, a fitted curve being a best-fit regression applied to athickness of the optical film as a function of layer number, the fittedcurve having an average slope K in a region extending across theplurality of interference layers, Δn/K greater than about 1.2.

Clause 200: In some examples of the optical film of clause 199, Δn/K isgreater than about 1.5.

Clause 201: In some examples of the optical film of clause 199, theoptical film having an optical density of greater than about 2.0 in thepredetermined wavelength range.

Clause 202: In some examples of the optical film of clause 199, theoptical film having an optical density of greater than about 3.0 in thepredetermined wavelength range.

Clause 203: In one example, an optical film comprising M sequentiallyarranged first unit cells optimized to transmit or reflect light in afirst, but not second, predetermined wavelength range, and Nsequentially arranged second unit cells optimized to transmit or reflectlight in the second, but not the first, predetermined wavelength range,each first and second unit cell comprising a lower index layer and anadjacent higher index layer, such that: for the M sequentially arrangedfirst unit cells, a ratio of an average of indices of refraction of thefirst layers to an average of indices of refraction of the second layerstimes M is greater than about 300; and for the N sequentially arrangedsecond unit cells, a ratio of an average of indices of refraction of thefirst layers to an average of indices of refraction of the second layertimes N is greater than about 300, wherein for light incident on theoptical film at any incidence angle from about zero degree to about 30degrees having any wavelength in the first and second predeterminedwavelength ranges, a ratio of an average optical transmittance T_(a) ofthe optical film for a first polarization state to an average opticaltransmittance T_(b) of the optical film for an orthogonal secondpolarization state is no less than about 1000,

Clause 204: In some examples of the optical film of clause 203, thefirst and second predetermined wavelength ranges are in respectivevisible and infrared ranges of an electromagnetic spectrum.

Clause 205: In one example, a polarizing beam splitter (PBS) comprisinga reflective polarizer disposed between and adhered to first and secondprisms, the reflective polarizer substantially reflecting polarizedlight having a first polarization state and substantially transmittingpolarized light having an opposite second polarization state, such thatwhen an incident light having a pre-determined wavelength enters the PBSfrom an input side of the PBS and exits the PBS from an output side ofthe PBS after encountering the reflective polarizer at least once, aratio of an average intensity of the exiting light to an averageintensity of the incident light is: greater than about 90% when theincident light has the first polarization state; and less than about0.2% when the incident light has the second polarization state.

Clause 206: In some examples of the PBS of clause 205, at least one ofthe first and second prisms is polymeric.

Clause 207: In some examples of the PBS of clause 205, the reflectivepolarizer comprises N sequentially numbered layers, N an integer greaterthan 50, each layer having an average thickness less than about 200 nm,a fitted curve being a best-fit regression applied to a thickness of theoptical film as a function of layer number, an average slope of thefitted curve in a region extending from the first layer to the Nth layerbeing less than about 0.2 nm.

Clause 208: In some examples of the PBS of clause 205, thepre-determined wavelength is in a range from about 400 nm to about 700nm.

Clause 209: In some examples of the PBS of clause 205, the reflectivepolarizer comprises an optical film as described in any of the precedingclauses.

Clause 210: In one example, an optical system for displaying an objectto a viewer centered on an optical axis and comprising: one or moreoptical lenses having a non-zero optical power; a reflective polarizerdisposed on and conforming to a first surface of the one or more opticallenses, the reflective polarizer substantially transmitting light havinga first polarization state and substantially reflecting light having anorthogonal second polarization state; and a partial reflector disposedon and conforming to a different second surface of the one or moreoptical lenses, the partial reflector having an average opticalreflectance of at least 30% for a predetermined wavelength range, suchthat an average optical transmittance of the optical system for anincident light along the optical axis having the second polarizationstate is less than about 0.1%.

Clause 211: In some examples of the optical system of clause 210, thereflective polarizer comprises N sequentially numbered layers, N aninteger greater than 50, each layer having an average thickness lessthan about 200 nm, a fitted curve being a best-fit regression applied toa thickness of the optical film as a function of layer number, anaverage slope of the fitted curve in a region extending from the firstlayer to the Nth layer being less than about 0.2 nm.

Clause 212: In some examples of the optical system of clause 210, thefirst surface of the one or more optical lenses is curved along at leasta first direction.

Clause 213: In some examples of the optical system of clause 210, thesecond surface of the one or more optical lenses is curved along atleast a first direction.

Clause 214: In some examples of the optical system of clause 210, eachof the first and second surfaces is curved along two mutually orthogonaldirections.

Clause 215: In some examples of the optical system of clause 210, thereflective polarizer comprises an optical film as described in any ofthe preceding clauses.

Clause 216: In one example, an optical stack comprising: a reflectivepolarizer comprising a plurality of interference layers, eachinterference layer reflecting or transmitting light primarily by opticalinterference, for a substantially normally incident light having apredetermined wavelength, the plurality of interference layers having anoptical transmittance greater than about 85% for a first polarizationstate, an optical reflectance greater than about 80% for an orthogonalsecond polarization state, and an optical transmittance less than about0.1% for the second polarization state; and an absorbing polarizerbonded to and substantially co-extensive with the reflective polarizer,for a substantially normally incident light having the predeterminedwavelength, the absorbing polarizer having a first optical transmittancefor the first polarization state, an optical absorption greater thanabout 50% for the second polarization state, and a second opticaltransmittance for the second polarization state, a ratio of the secondoptical transmittance to the first optical transmittance being greaterthan about 0.001.

Clause 217: In some examples of the optical stack of clause 216, thepredetermined wavelength is about 550 nm.

Clause 218: In some examples of the optical film of any one of the aboveclauses, the predetermined wavelength range of the optical film is fromabout 430 nm to about 465 nm, 490 nm to about 555 nm, and about 600 nmto about 665 nm.

Clause 219: In some examples of the optical film of any one of the aboveclauses, the predetermined wavelength range of the optical film is fromabout 400 nm to about 430 nm, 450 nm to about 500 nm, and about 550 nmto about 600 nm.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. An optical stack comprising: a reflectivepolarizer comprising a plurality of polymeric layers, each polymericlayer having an average thickness less than about 200 nm; and anabsorbing polarizer bonded to and substantially co-extensive with thereflective polarizer, such that for a substantially normally incidentlight and at least one predetermined wavelength in a range from about400 nm to about 700 nm and about 800 nm to about 1300 nm: the pluralityof polymeric layers has an optical transmittance greater than about 90%for a first polarization state, an optical reflectance greater thanabout 90% for an orthogonal second polarization state, and an opticaltransmittance less than about 0.1% for the second polarization state;and the absorbing polarizer has a first optical transmittance for thefirst polarization state, an optical absorption greater than about 50%for the second polarization state, and a second optical transmittancefor the second polarization state, a ratio of the second opticaltransmittance to the first optical transmittance being greater thanabout 0.01.
 2. The optical stack of claim 1, wherein the ratio of thesecond optical transmittance to the first optical transmittance isgreater than about 0.1.
 3. The optical stack of claim 1, wherein the atleast one predetermined wavelength comprises 550 nm.
 4. The opticalstack of claim 1, wherein the plurality of polymeric layers comprises aplurality of alternating different first and second polymeric layers. 5.The optical stack of claim 1, wherein for light incident at an incidenceangle of about 30 degrees and for the at least one predeterminedwavelength, the plurality of polymeric layers has an opticaltransmittance greater than about 85% for the first polarization state,an optical reflectance greater than about 80% for the secondpolarization state, and an optical transmittance less than about 0.2%for the second polarization state.
 6. The optical stack of claim 1,wherein a total number of the polymeric layers in the plurality ofpolymeric layers is less than
 800. 7. The optical stack of claim 1,wherein for the substantially normally incident light and a wavelengthrange from about 400 nm to about 700 nm, the reflective polarizer has anaverage optical transmittance T_(a) and an average optical reflectanceR_(a) for the first polarization state, and an average opticaltransmittance Tb and an average optical reflectance Rb for the secondpolarization state, Tb/Rb less than about 0.002 and Ra/Ta less thanabout 0.17.
 8. The optical stack of claim 7, wherein T_(a)/T_(b) isgreater than about
 425. 9. The optical stack of claim 7, whereinR_(b)/R_(a) is greater than about 6.7.
 10. The optical stack of claim 1,wherein the reflective polarizer has a thickness of less than about 60μm.
 11. The optical stack of claim 1, wherein the polymeric layers inthe plurality of polymeric layers are sequentially numbered from 1 to N,N an integer greater than 200 and less than 1000, a fitted curve fittedto the N polymeric layers by a best-fit regression applied to a layerthickness profile of the polymeric layers plotting a thickness versus anumber of each polymeric layer, has an average slope across the N layersof less than about 0.2 nm/layer.